Minimax Estimation of Budgeted Treatment Value Curves with Discrete Covariates
The verified matched rate is a substantial contribution, but the central statistical mechanism needs a clearer explanation before the paper is ready for a leading journal.
- Minimax risk for the budget-value curve The main text names pilot localization, Jackson approximation, and factorial moments but gives little explanation of how they produce the logarithmic improvement or control all shadow prices. Readers must work through the long technical appendix to understand the paper's central statistical contribution.
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- Submitted
- 29 Sep 2026 (v1) · last revised 29 Sep 2026 (v4)
- Cite as
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CSWP-2026-024· https://causalsmith.org/papers/stat_discrete_budgetvalue_curve_v1/
@techreport{causalsmith_stat_discrete_budgetvalue_curve_v1,
title = {Minimax estimation of budgeted treatment value curves with discrete covariates},
author = {{CausalSmith}},
year = {2026},
month = sep,
institution = {CausalSmith Working Papers},
number = {CSWP-2026-024},
url = {https://causalsmith.org/papers/stat_discrete_budgetvalue_curve_v1/},
note = {Version 4, 29 Sep 2026. Machine-generated; formal statements verified in Lean 4 at commit c4f4de3}
} https://causalsmith.org/papers/stat_discrete_budgetvalue_curve_v1/ Cites version 4 of 29 Sep 2026. Abstract
We study the population oracle-value curve indexed by treatment capacity for a binary treatment and outcome on a known discrete covariate alphabet. Under independent sampling, consistency built into the observation map, conditional exchangeability, and fixed treatment overlap, we characterize the finite-sample minimax risk for estimating the curve over any closed interval of budgets symmetric about one half. For every sample size , alphabet size , and interval endpoint , the all-procedure expected squared supremum risk on is of order , with constants depending only on overlap. A specified Jackson–factorial estimator attains the upper bound by estimating one shadow-price process and then recovering the entire curve through a dual minimum. A matching lower bound holds at half capacity within a family whose occupied-cell treatment effects are positive, whose capacity binds, and whose full-capacity value is fixed. The result includes simultaneous estimation over every budget from zero to full capacity at the same minimax rate as the unrestricted full-capacity scalar value.
Introduction
A treatment capacity turns population value into a curve: each budget specifies the largest expected outcome attainable by a feasible assignment policy. Estimating that curve addresses questions about the value of additional capacity while allowing the most valuable recipients to change with the budget. This paper characterizes the finite-sample precision of that population target for binary treatment and outcome on a known discrete covariate alphabet that may grow with sample size.
Let be the known number of covariate cells, the number of independent observed records, and a fixed treatment-overlap parameter. At budget , the oracle value is the maximum population outcome under policies whose average treatment share is at most , for a causal law satisfying consistency, conditional exchangeability, and overlap. We measure estimation error by the expected squared largest error over , the budget interval with endpoint parameter , and compare all measurable curve estimators. For every , , and , Theorem 1 establishes the risk order with comparison constants depending only on . The statement includes the full interval and the single half-budget value.
The upper bound uses a dual representation of each budget value as the minimum of a common shadow-price process plus the capacity charge, as shown in Proposition 1. A pilot-local Jackson polynomial and factorial-moment statistics estimate that process across shadow prices; conditional averaging yields a curve estimator based on the observed sample in Algorithm 1. The dual-representation proposition, Proposition 1, gives the factor-one contraction from uniform process error to curve error; Theorem 3 gives the resulting estimator risk guarantee. This contraction lets estimation of the whole curve attain the minimax rate of the unrestricted full-capacity scalar value. The guarantee applies across the stated causal law class, including null cells, unequal occupied-cell masses, boundary outcome means, and treatment-effect ties.
The matching converse comes from a paired causal family. At half capacity, every occupied-cell treatment effect lies between and , the available capacity is used, and the full-capacity value equals . In this family, the target obeys the affine identity , where is the dual threshold process. An exact map sends paired samples from two unknown discrete distributions to observations from this causal family. Thus, an estimator of the half-budget value would yield an estimator of their distance, giving the lower bound from Jiao et al. (2018). The full-capacity coordinate, when included in the interval, is the unrestricted scalar oracle-value target studied by CausalSmith (2026).
The analysis connects constrained-allocation value processes (Feng et al., 2026) and uniform inference for optimized value functions (Firpo et al., 2023) with large-alphabet functional estimation by polynomial approximation and moment matching (Jiao et al., 2015; Cai et al., 2011). Its risk criterion concerns the optimized population value across budgets; policy-learning work evaluates the welfare of an estimated assignment rule (Kitagawa et al., 2018; Athey et al., 2021; Pellatt, 2023). The formal statements and internal proofs are machine-checked in Lean 4, with verification scope recorded in the appendix.
The remainder first develops the connections to related work, then defines the causal class, budget value, and risk criterion. It next states the matched rate and summarizes the estimator, followed by discussion and limitations. The appendices give the supporting process bounds, lower-bound reduction, and verification scope.
Related work
The budget-indexed oracle value connects treatment allocation under a capacity constraint with inference for optimized value functions. Feng et al. (2026) derive an asymptotic value-process law for binary constrained allocation using differentiability of the sorting operator, a regular decision boundary, and joint process convergence. Their conclusion concerns the limiting distribution of a plug-in process in that regular regime. Here, for a known -cell alphabet and fixed overlap, the estimand is the same type of oracle capacity curve, but the conclusion is a finite-sample minimax bound for expected squared supremum loss over every symmetric budget interval. When is fixed the risk is of order ; when grows it is of order . The causal law class permits positive-mass treatment-effect ties at decision thresholds. Firpo et al. (2023) develop uniform tests for marginally optimized value functions using directional derivatives and resampling. Their optimization framework is more general, while the present result gives a rate for the particular causal capacity curve under fixed overlap. Sverdrup et al. (2025) evaluate targeting across budgets with multiple treatment arms using Qini curves and asymptotic pointwise confidence intervals at specified budgets. Our target optimizes the population policy separately at each budget and our loss compares an estimated curve with that oracle curve.
Bhattacharya et al. (2012) study welfare from a data-based binary allocation under a budget constraint and give asymptotic confidence intervals for that policy’s welfare. Luedtke et al. (2016) analyze differentiability and inference for the mean outcome under an optimal individualized rule, including nonunique optima. Hirano et al. (2009) develop asymptotic comparisons of statistical treatment rules. These results frame allocation and optimal-value inference; here the estimand is the population oracle optimum at every budget in , and the guarantee is an all-procedure finite-sample minimax bound for expected squared supremum loss under fixed overlap and a known discrete alphabet. Policy-learning work instead assesses the welfare of a selected rule (Kitagawa et al., 2018; Athey et al., 2021; Pellatt, 2023). The unrestricted discrete scalar result (CausalSmith, 2026) studies the coordinate under the same causal class and has the same minimax order . The factor-one dual contraction in Proposition 1 shows that estimating every coordinate in attains that order simultaneously, including when .
The statistical tools also connect to estimation of functionals on large discrete alphabets. Polynomial approximation and factorial-moment statistics support estimation of nonsmooth functionals (Jiao et al., 2015), while moment matching supplies lower bounds for such problems (Cai et al., 2011; Jiao et al., 2018). Here, polynomial approximation is applied to cell contributions across shadow prices, and paired-cell moment matching captures the difficulty of estimating the capacity-indexed value.
Setup and assumptions
Let denote the known number of covariate cells, with , and let denote their index set. The sample size is ; we use for a cell index and for an arm index in . For nonnegative sequences, means , where is independent of but may depend on fixed overlap; denotes the corresponding two-sided comparison. The norm is the supremum norm on the indicated domain.
Let be a full-data causal law for the covariate , treatment , and potential outcomes . Treatment selects the observed outcome , so an observed record is . The observation map makes the relation between the full-data law and its observed margin explicit. For the observed sample , we impose independent superpopulation sampling.
The observed records are independent and identically distributed under the observed margin of .
⊢ LeanIndependent superpopulation sampling makes the observed margin the common law of every record and supplies the product-law experiment used in the risk criterion (van der Vaart, 1998). The identification conditions concern how that margin relates to potential outcomes. First, consistency connects each recorded outcome to the potential outcome under the received treatment.
almost surely.
⊢ LeanConsistency is the standard link between observed and potential outcomes (Hernán et al., 2020). The observation map records this link atomwise.
Under , .
⊢ LeanConditional exchangeability then relates treatment assignment to the two potential outcomes within each covariate cell.
For , let be a full-data causal law on , where ranges over a -element alphabet and . The associated full observation is defined atomwise by The observed margin of is the law of .
⊢ LeanConditional exchangeability permits arm-specific observed outcome means to identify the corresponding cell potential-outcome means (Rosenbaum et al., 1983). To state the remaining restriction precisely, we record cell masses and propensities.
For a discrete law on a covariate alphabet of size , the observed mass of cell is
⊢ LeanFor a discrete observed-data law on a -cell covariate alphabet and a sample size , the product law is the joint law of independent records drawn from . For each occupied cell , write and define its treatment propensity by .
⊢ LeanThe cell mass determines whether a conditional quantity in cell is relevant to population value.
For every with , the treatment propensity satisfies
⊢ LeanThe known alphabet fixes the cells over which policies are optimized; cell probabilities may be arbitrarily small, so the law class includes rare cells and cells absent from a sample. Binary outcomes give the observed arm-and-outcome categories used by the factorial-moment estimator. For each occupied cell, the treatment propensity lies in the band set by the fixed overlap parameter , where . This condition supports identification of both cell means (Rosenbaum et al., 1983) and places no lower bound on a cell’s probability. The risk constants depend only on fixed overlap; the paired lower-bound family uses propensity in every occupied cell. Consistency is encoded by the observation map, which records the observed outcome as .
, for each integer , is the class of laws satisfying:
⊢ LeanThe class fixes the covariate alphabet, binary variables, and identification conditions for the minimax comparison. We next specify how a population treatment capacity restricts randomized policies.
⊢ Lean
A policy assigns each cell a treatment probability . At population capacity , its average treatment share is constrained by the cell masses; the resulting feasible class is . The value of assigning every cell to control supplies the baseline for evaluating these policies.
For a full-data law , let and let on occupied cells, with on null cells. The population value of assigning every cell to control is
Population value depends on the arm-specific potential-outcome mean in each occupied cell and on the cell treatment effect . The control-policy value provides the baseline for evaluating feasible policies.
For a full-data causal law on a -cell covariate alphabet, an arm , and a cell , let . On occupied cells, where , define On null cells, where , set .
⊢ LeanFor a full-data causal law on a -cell covariate alphabet and a cell , define the cell treatment effect by where is the potential-outcome mean for arm in cell .
⊢ LeanThe zero convention gives on null cells and leaves every population value unchanged.
These cell quantities determine the maximum population value attainable at each budget.
The maximum population value at budget and the budget-indexed oracle-value curve on are
⊢ LeanFix an endpoint parameter and write for the closed budget interval. Maximizing over feasible randomized policies gives the budget value and its curve on .
To express this value through the observed margin, we use treatment-outcome masses within each cell and their arm totals.
For , define the mass in treatment arm and the total mass by
For each cell, let the observed four-mass vector have coordinates , for . Its entries encode the observed treatment-outcome distribution without conditioning on a possibly null cell. For a generic nonnegative four-vector , write for its arm mass and for its total mass.
The finite full-data support can equivalently be indexed by potential atoms.
For a covariate alphabet of size , a potential atom is an element of
⊢ LeanA shadow price converts the capacity constraint into a threshold comparison within each cell. The stabilized arm contribution , threshold contribution , and aggregate process express that comparison in observed masses.
For , define the stabilized arm contributions, cell contribution, and dual threshold process by When all four cell masses vanish (), the quotient defining takes the value zero: .
⊢ LeanWe say the half-budget constraint is binding for when there exists an optimal policy such that
The zero convention in Definition 12 gives and covers empty covariate cells.
Under Assumptions 3 and 4, the stabilized arm contribution at an occupied cell equals . The threshold contribution therefore combines control value with the positive part of the cell treatment gain after charging the shadow price for treatment capacity. The following identity turns those cellwise contributions into the population budget value.
Let be a full-data causal law with observed margin. Suppose:
Alphabet size. The known covariate alphabet has size .
Overlap parameter. The fixed overlap parameter satisfies .
Model membership. as defined in Definition 4.
For , write for the dual threshold process formed from the observed margin of . Then, for every , the budget value of Definition 9 satisfies Moreover, for every process bounded on ,
⊢ LeanThe identity represents every budget value as the lower envelope of the same shadow-price process plus . Its second assertion transfers a uniform process error bound to a uniform curve error bound with factor one, so a single estimated process serves the entire budget interval. The identity and contraction concern the optimized value and permit multiple maximizing policies or minimizing shadow prices.
The observed sample collects the records on which a curve estimator may depend.
For , the observed sample consists of observed records , each with in the -element covariate alphabet.
⊢ LeanWe assess curve estimation by the all-procedure expected squared supremum risk . The criterion compares bounded-function-valued estimators over the causal law class and the closed interval .
For , set . The all-procedure expected squared supremum risk is where the infimum ranges over all measurable maps from the observed sample into bounded functions on .
⊢ LeanBoth endpoints belong to . In particular, gives the full interval , while gives the single budget .
Minimax risk for the budget-value curve
The shadow-price representation in Proposition 1 reduces estimation of the budget-value curve to estimation of one process. The resulting minimax risk is matched for every interval , including the full budget range and the single half-budget value.
Fix an overlap parameter . There exist constants such that, for every , , and , the curve minimax risk of Definition 15 satisfies For every measurable scalar estimator based on the observed records, there is a full-data law with the following properties:
(Causal model.) , and each occupied cell has , , and .
(Values and binding capacity.) , and there is a policy such that
(Scalar risk.) Under independent observations from the observed margin of ,
When , every also satisfies the full-budget identity where is the budget value of Definition 9.
⊢ LeanThe upper bound applies to all budgets in the chosen interval simultaneously. In the paired family, the half-budget coordinate attains the stated risk order with positive occupied-cell effects, binding capacity, and a full-capacity value fixed at . This family makes the allocation problem visible through the ranking of cell benefits. Simultaneous curve estimation therefore attains the unrestricted full-capacity scalar minimax order under the stated conditions. The reduction uses the bound for estimating the distance between two unknown discrete distributions from Jiao et al. (2018).
The proof has three steps. First, the shadow-price identity reduces all budget values to one threshold process, and taking a minimum is a contraction in supremum norm. Second, the estimator below controls that process cell by cell: empirical masses suffice for a small alphabet, while pilot localization and factorial moments handle a growing alphabet. Third, the paired family converts the half-budget value into a discrete two-sample functional, giving the matching lower bound. The appendix contains the polynomial and process estimates behind the second step.
The exact estimator and its uniform upper-bound theorem are stated in the technical appendix, Algorithm 1 and Theorem 3. Its statistical construction is summarized here.
The estimator first estimates one threshold process across shadow prices, then takes a shadow-price minimum to obtain each budget value. For a small alphabet it inserts empirical cell masses into that process; with a larger alphabet and adequate sample size, pilot counts localize each mass and evaluation counts estimate a local Jackson polynomial by factorial moments. Clipping controls the cell estimates before they are summed, and the sparse-sample branch reports a constant curve. The displayed construction uses an exact conditional average over auxiliary permutations and markings. Its polynomial degree and pilot-width constants serve the risk proof: at ordinary alphabet sizes the degree remains two and the pilot intervals are broad. The rate is a theoretical benchmark for this exact estimator.
In the Jackson–factorial branch, write . Pilot counts set cell-specific localization widths; on each resulting rectangle, the Jackson approximation error is bounded by radius-dependent terms divided by the polynomial order and Lemma 3. Independent evaluation counts turn the polynomial terms into factorial-moment estimates. The resulting cell bias is bounded by uniformly over shadow prices, while the centered good-pilot process has expected squared supremum error of order ; the bad-pilot envelope has an exponentially small factor in Theorem 4. Summing the bias over cells and combining it with these fluctuation bounds yields the same process-risk order. The empirical branch covers small alphabets, and the constant branch covers the sparse-sample regime.
Conditional averaging makes the exact curve-valued estimator a function of the observed sample. By Proposition 1, the error in each budget value is bounded by the uniform error of the estimated threshold process. The same process estimate therefore controls the supremum over .
The bound measures the squared largest error across the interval before taking expectation, so it also applies when a budget is selected after viewing the estimated curve. The process bound behind it is given in the appendix; the dual identity transfers that bound to budget values without an additional cost for considering several budgets.
The matching converse can be stated directly for estimation at half capacity. It retains positive effects throughout the occupied cells and fixes the value under full provision.
Fix an overlap parameter . There exists such that, for every , , every collection of observed-data laws satisfying Assumption 1 for each full-data law, and every measurable scalar estimator based on the observed records, there is a full-data law satisfying:
(Model class.) .
(Full-budget value.) , with as in Definition 9.
(Effects in occupied cells.) For every cell , implies .
(Binding capacity.) The half-budget constraint is binding for .
For this law,
⊢ LeanPositive treatment effects make the half-budget allocation use its available capacity, while differences across cells determine which recipients are most valuable. The theorem establishes the lower risk benchmark in this capacity-active setting even with the full-budget value fixed. Its reduction again invokes the discrete bound of Jiao et al. (2018).
Two special cases put the general rate and the budget curve in familiar terms: a fixed covariate alphabet and a common positive effect across occupied cells.
Fix the overlap parameter and the known covariate alphabet size under the following conditions:
(Overlap.) .
(Alphabet.) .
For the curve minimax risk in Definition 15, there are constants with such that, for every and every ,
Moreover, let belong to the causal model class in Definition 4. Write for the mass of cell , for its arm- potential-outcome mean, and for its treatment effect. If some satisfies in every cell with , then, for every and every , the budget value in Definition 9 satisfies
⊢ LeanWith the alphabet and overlap parameter fixed, the matched rate is . Under a common positive effect, every unit of treatment capacity adds the same population value, giving a linear budget-value curve. In the common-effect clause of Proposition 2, the symbol denotes an arbitrary positive treatment effect; it is independent of the lower comparison constant also written in the risk bound.
Discussion and limitations
The risk in Definition 15 measures expected squared supremum error over the budget interval . Thus, Theorem 3 gives a simultaneous guarantee for one estimated value curve. When , that guarantee covers every budget from zero to full population capacity. Together with Theorem 2, the upper bound identifies the minimax rate under the stated conditions.
When is small, the minimax risk has that order; when the ratio is large, it has constant order. The minimax rate contains a logarithmic factor, and the upper bound uses polynomial estimation of the discrete threshold process. In the paired family, differences among positive cell benefits determine their ranking and hence the half-budget allocation value, even as the full-budget value stays fixed. Under Theorem 2, this single coordinate attains the curve’s risk order. The factor-one dual contraction carries the process estimate to all budgets, and the whole curve attains the unrestricted full-capacity scalar minimax order.
Limitations and future work
The global supremum criterion covers the endpoint when ; a budget-local analysis could characterize risk as the budget shrinks with sample size. Adaptive simultaneous bands call for a coverage criterion, while policy regret calls for evaluating an estimated allocation. The theorem’s estimator is the exact conditional average in Algorithm 1; approximating that average by Monte Carlo draws would require a separate draw-count and approximation-error guarantee before claiming the same rate. Other directions include covariate alphabets learned from data and allocation across multiple treatment arms.
Appendices
Proofs and verification scope
Estimator and uniform upper bound
The observed category-cell masses specify the inputs to the exact Jackson–factorial construction.
For a covariate cell and a treatment-outcome category , define These four masses are the components of the observed cell vector .
Given , , and , the estimator uses the tuning quantities defined below.
Set Index treatment-outcome categories by .
If , form the empirical category-cell masses and threshold process: Proceed to the final step.
If and , output In the remaining branch, and , draw independently of . On , set On , uniformly permute the records, retain the first , and independently mark each retained record pilot or evaluation with probability each. Define the pilot and evaluation counts by where denotes the th record in the uniform permutation.
On , for every and , set All radii are strictly positive. Let and . Define the normalized positive order-four Jackson kernel by where the quotient takes its continuous value at zero and is the unique normalizing constant. Set . For each and , define the unique tensor polynomial , of coordinatewise degree at most , through and define its coefficients by the unique expansion For integers , define The cell estimate, its clipped version, and the auxiliary threshold process are Here In this branch, average the auxiliary process conditional on the observed sample:
In the empirical and Jackson–factorial branches, report The output uses the minimum value and requires no optimizer selection. If an implementation stores an optimizer, it stores the least element of the nonempty compact argmin set. These branch rules, the zero process on , and the least-minimizer convention apply under every data or treatment-effect tie.
The conditional average in Algorithm 1 is an observed-sample statistic. The dual contraction transfers a uniform process bound to every budget in .
Fix the overlap parameter . Suppose:
(Overlap.) .
(Sample and alphabet.) and .
(Budget interval.) , and .
(Sampling.) For each causal law , the observed records follow Assumption 1 for the observed margin of .
There is a constant , depending only on , such that the estimator in Algorithm 1 and the budget value in Definition 9 satisfy
⊢ LeanThe estimator controls the threshold process over the full interval of shadow prices before taking the dual minimum. Since the minimum value is Lipschitz in the supremum norm of that process, one process bound controls every budget in , including zero and full capacity when .
Process estimates
The upper-bound analysis begins with regularity of the cell contribution in the dual representation of Definition 12. Bounded variation controls its dependence on the full interval of shadow prices.
For , there is a finite constant such that, for every , where .
⊢ LeanFix , and write In particular, . For either arm , the stabilized contribution in Definition 12 satisfies Here is a derivation of the second bound, including zero masses. Put and , and define analogously. When , the two branches are They agree at equality; when , . If both vectors use the first branch, their difference is at most . If both use the second, , and Since and , splitting the difference of the two products bounds it by .
For the mixed case and , the identity and the bounds give the upper bound below. The rearrangement shows that its left-hand side has absolute value at most , since . Consequently, For the lower bound, return to the first mixed-case identity: its correction term is nonnegative. Hence the difference is at least . Interchanging handles the other mixed case. Finally, if either total mass is zero, all its coordinates and its arm contribution vanish; and give directly. The same inequalities also establish in every branch.
Define the positive gain and its hinge by and similarly for . The arm bounds give and . Because on , Taking positive parts and using the arm contribution bound yields
Set Both breakpoints lie in , including when a total mass vanishes. The positive-part inequality gives, throughout that interval, If , the three successive affine expressions for are on , , and , respectively. If , they are on , , and . The formulas agree at their shared endpoints, also for coincident breakpoints. Variation on each affine piece equals the absolute difference of its endpoint values, which is at most by the preceding pointwise bound. Adding the three pieces gives
The constant in leaves variation unchanged. At , the positive-part inequality and the arm contribution bound give Thus the positive-gain and variation bounds, together with , imply The displayed finite, nonnegative coefficient supplies .
∎The bound in Lemma 1 supplies a common regularity measure across shadow prices. The process criterion below collects the corresponding approximation, bias, and fluctuation bounds for the estimator in Algorithm 1.
For fixed , the uniform process handle is the set of constants satisfying the five groups of bounds below for the single pilot-local Jackson polynomial and clipping rule of . Membership requires the bounds simultaneously for every in the Jackson–factorial branch, every observed categorical law on the known -cell alphabet, every pilot realization, every cell , and every .
Set For the expectations and norms below, use the uncapped marked-Poisson experiment in which all pilot and evaluation counts and are mutually independent with distribution . Define Evaluate , , and in this experiment. The membership bounds are:
Coefficient envelope and exponential bound.
Centered process on the pilot event.
Cellwise bias.
Cellwise envelope outside the pilot event.
Centered process outside the pilot event.
The criterion in Definition 17 treats pilot localization and its complement within the same process bound. A second-moment bound for the pilot radii supplies an integrability input for that criterion.
Let , , and . Let be a categorical law on the -cell alphabet, with category-cell masses and cell masses , and fix a cell . In the ideal Poisson experiment, the pilot counts are independent with means . Let be the sum of the four pilot radii in Algorithm 1, and set Then is integrable under the ideal Poisson law, and
⊢ LeanSince and , we have and . For each , the localization intervals in Algorithm 1 give Both and are nonnegative. The maximum in the last expression lies between and ; hence . Applying yields
There are four categories in . Cauchy–Schwarz and the coordinate bound therefore give, pointwise,
Each pilot count is integrable under its Poisson law, with The pointwise bound thus proves integrability of and gives Finally, and , so Combining the two inequalities proves .
∎The bound in Lemma 2 controls the random localization scale by cell mass and the logarithmic alphabet factor. On a localization rectangle, the Jackson approximation has the following coordinatewise bound, including at its boundary.
Let be the local polynomial for of Definition 12, formed by the normalized order-four Jackson construction in Algorithm 1 with pilot center and radii replaced by and , and with the value added to the normalized polynomial evaluation. Suppose that:
(Parameters.) The overlap parameter satisfies , the shadow price satisfies , and is a positive integer.
(Rectangle.) For every , and .
(Evaluation point.) For every , .
Then
⊢ LeanSet for . The rectangle assumption makes both vectors nonnegative. We first establish
For each arm , the contribution in Definition 12 satisfies Here is the scalar estimate behind this bound. At zero total mass, every coordinate vanishes. We evaluate the quotient defining in Definition 12 with the convention , so . Since , and likewise for , the claim follows whenever either vector has zero total mass. For positive total masses, the defining maximum gives when , and in the other regime. When both vectors are in the first regime, their difference is bounded by . When both are in the second, and Expanding the difference of the two products, using and , proves the displayed arm bound.
For the mixed regime in which is in the first regime and in the second, the difference equals The second term is nonnegative. Its ratio lies in , and the two regime inequalities imply Consequently the difference lies between and . Interchanging the vectors covers the remaining mixed regime.
Finally, is one-Lipschitz. Applying this to the hinge in Definition 12 gives Since , is continuous on .
Write for the centered coefficients in Algorithm 1 with its pilot center and radii replaced by . Explicitly, they are the unique coefficients satisfying The normalized polynomial is therefore The continuity just proved applies to on . The normalized construction, including the added center value, therefore gives, for every , The order-four kernel has trigonometric degree in each coordinate, so has coordinatewise polynomial degree at most . Positive radii permit the affine substitution which preserves those coordinatewise degree bounds and identifies this polynomial with the one in the statement.
Put The evaluation-point assumption makes every angle well defined in , and . Positivity and unit integral of each , followed by the Lipschitz estimate from the first step, yield The cosine addition formula and , give
For completeness, the kernel moments used here obey Indeed, writing , the unnormalized fourth power in Algorithm 1 is . Orthogonality of the Fourier modes gives For , the inequality , together with , bounds its weighted second integral by . Normalization and thus give the sharper second-moment bound . Integrating gives a first-moment bound ; the displayed bounds follow for every positive integer .
Integrating the cosine estimate coordinatewise now gives Finally, Substitution proves the asserted bound, including points on the faces of the rectangle.
The endpoint factors in Lemma 3 make the approximation bound sensitive to the evaluation point’s position within the pilot rectangle. To control observations outside the good-pilot event, the next lemma bounds moments of the pilot discrepancy and width together.
Let , let be an observed categorical law on the -cell alphabet, and fix a cell . Write for its four category-cell masses and . Set and .
Suppose the four pilot counts are independent, with for each . Form and as in Algorithm 1, and let be the quarter-halfwidth pilot event of Definition 17. Define For each ,
⊢ LeanFor each and , define and let Here and , including when . The following scalar estimates hold also when : For the first estimate, a count in with satisfies one with satisfies For the upper tail, gives , so the defining threshold exceeds the stated Bernstein threshold. For the lower tail, the bad-event condition gives . Since , Moreover, Thus ; positivity of the deviation gives . The upper and lower Poisson Bernstein bounds at level give for each tail.
For the moment estimate, put . Since and , The middle expression is the centered Poisson exponential moment; the last inequality uses . Applying to the nonnegative exponent and for yields the stated moment estimate.
For , the elementary square inequality gives Taking expectations and using the two estimates above gives
Define For , the preceding truncated moment applies when . When , independence factors the expectation, and the probability and ordinary moment estimates apply. Thus, in both cases, All scores are nonnegative, so the four-term power inequality and the union bound yield Since , Cauchy–Schwarz and nonnegativity give Consequently, The final coefficient comparison holds for each of , and gives .
By Algorithm 1, for every , The event in Definition 17 therefore satisfies : failure of its quarter-halfwidth condition requires a deviation greater than , which exceeds the threshold defining . Pointwise, Finally, . Applying the preceding product moment bound proves
The exponential factor in Lemma 4 controls the contribution of bad pilot localizations. Across cells, bounded variation gives a maximal inequality for the centered paths on either part of the pilot split.
Let be nonnegative integers, let , and let be a discrete law on the -cell alphabet with category-cell masses . In the ideal count experiment of Definition 17, the pilot and evaluation counts and are mutually independent with laws, where . Choose the pilot events uniformly across cells: either for every , or for every , with as in Definition 17. For each cell , define the path on by where is the clipped cell estimate of Algorithm 1 and is defined in Definition 12. Assume:
(Regularity.) For every count table and cell , is continuous in . For each , the count-table map into is measurable and Bochner integrable.
(Finite variation.) For each , almost surely.
(Second moments.) For each , is integrable.
(Independence.) The paths are independent.
Then
⊢ Lean1. Set up the count law and path envelopes. Let be the joint law of the pilot and evaluation count tables in Definition 17. For a count table , write for the path in the statement and set The second-moment assumption makes both and integrable. The regularity assumptions give Bochner-integrable paths, and the independence assumption applies to their joint law. These observations also cover , when every sum below is empty.
2. Reduce the centered sum to signed differences. Take independent count tables with law , and define, for and , Let be independent uniform signs, independent of the count tables, and define their signed supremum energy by Jensen’s inequality applied to the independent copy gives The pairs are independent across . Swapping either entry of any pair preserves their joint law and reverses the sign of its difference. Averaging these equalities over all sign choices therefore yields All these expectations are finite by the second-moment assumption.
3. Bound the signed supremum for fixed count tables. Fix a pair for which every has finite variation. Let , , be the cumulative variation of from to . Continuity and finite variation give a continuous, nondecreasing control satisfying Define the common control on by Since ,
Choose ordered, compatible dyadic control quantiles , for and , so that Such choices follow from continuity of . For each sign vector, let By Equation 1, every edge at level has squared coefficient sum at most . For , , and , write When , each edge satisfies . For every , independence of the signs and the elementary bound give Applying this bound to both signs, choosing , and taking the union over edges gives, for , Set . Integrating the tail above yields When , Equation 1 makes every edge increment zero. Thus in every case The numerical factors in Equation 2 have a summable square root: Here the termwise bound follows from and .
To reconstruct the signed path, for each and define These lower dyadic indices start at zero, satisfy , and obey The parent grid point equals the even child by compatibility; the odd child differs by one adjacent edge. At level zero the grid point and have the same control value, so Equation 1 makes their path coordinates equal. Telescoping therefore gives, for every , where the sum is empty at . The control values of and differ by at most . Applying Equation 1 in whichever order these two times occur gives Hence the finite signed sums along the chain converge to their value at , including on flat parts of the control. If , the same control bound makes all constant and the conclusion is immediate. Passing to the limit and taking the supremum over gives Sign orthogonality, the triangle inequality, and Equations 2 and 3 imply Finally, the triangle inequalities for the supremum norm and total variation give
4. Average the pointwise bound. Integrating the last inequality over the two independent count tables and using their identical laws gives Combining this with the two relations in Step 2 proves the stated inequality.
∎By Lemma 5, cellwise path moments yield control uniform in the shadow price. The reported estimator averages over auxiliary draws from an observed sample; the following identity relates that average to the uncapped count experiment.
Fix and an observed categorical law on the -cell alphabet, with category-cell masses . Let . For , a permutation of the record indices, and pilot/evaluation marks , write for the pilot and evaluation count tables formed from the first permuted records according to Algorithm 1. Define In the uncapped marked-Poisson experiment, ; conditional on , draw independent records from and mark each independently as pilot or evaluation with probability , yielding count tables .
For every real-valued function of pairs of count tables that is integrable under the ideal law of Definition 17, whose pilot and evaluation category-cell counts are independent variables,
⊢ LeanLet , and let be the space of finite sequences of records in , each carrying a pilot or evaluation mark. Write for a sequence with law : , the are independent with law , and the independent marks are pilot or evaluation with probability each. Define by , where These are the count tables used in Algorithm 1. Partition the marked observation space into the singleton types , where . Each type has probability . For any array , the Poisson probability of the total count and the conditional multinomial probability of the singleton counts give Here , and zero powers use the usual convention . Grouping the singleton counts by mark gives ; the factorization shows that its pilot and evaluation coordinates are independent Poisson variables, each with mean . Its law is the ideal count law specified in Definition 17; the identity also covers zero cell masses and .
Set by . The preceding identification and the assumed integrability of give
For , define the marked prefix A permutation of an independent -sample remains an independent -sample, while a uniform mark vector gives each mark probability . Consequently, at every whose Poisson probability is positive, Integrability under supplies integrability on each such count fibre; fibres with zero Poisson probability contribute zero. Multiplying by the respective Poisson probabilities and summing over therefore yields This is the finite count-fibre decomposition of the marked-Poisson expectation.
For every admissible prefix, the indicator sums defining agree coordinatewise with the permuted pilot and evaluation counts: Substitute this identity and into the preceding equality. Its left side has weight , and its right side is the stated nonoverflow expectation under the uncapped marked-Poisson experiment. When , there is no probability law on the empty observed alphabet, so the assertion quantified over is vacuous.
The identity in Lemma 6 supplies the count-law link for the conditional average. Together with the radius, approximation, bad-pilot, and maximal-path bounds, it supports a common constant for the process criterion and the threshold-process bounds.
Fix an overlap parameter . There is a single constant , belonging to the uniform process handle in Definition 17, for which the following conclusions hold whenever:
(Sample and alphabet.) , , and .
(Sampling.) The law of the observed records satisfies Assumption 1 for the observed margin of .
(Causal law.) The full-data law belongs to of Definition 4.
Write , , and . Simultaneously for every cell and every , the absolute bias of the uncapped Jackson cell estimate of is at most The expected squared supremum of the centered good-pilot error sum is at most . The uncentered bad-pilot cell envelope satisfies and the expected squared supremum of the centered bad-pilot error sum is at most . Finally, the ideal and averaged versions of the dual threshold process in Algorithm 1 each have expected squared supremum error relative to at most . The same applies to all these bounds.
⊢ LeanThe final process bounds in Theorem 4 apply to an entire interval of shadow prices. Through the dual representation in Proposition 1, they provide the simultaneous control used in Theorem 3, including budgets selected after the curve is estimated. The average is formed at the threshold-process level before optimization.
Two boundedness facts establish that the empirical and conditionally averaged threshold processes have finite values throughout the shadow-price interval.
For any , any real overlap parameter , and any sample of observations on the -cell alphabet, let be the empirical threshold process of Algorithm 1, with as in Definition 12. There exists such that
⊢ LeanFix and the sample. For each cell , Definition 12 and Algorithm 1 give, for , The empirical vector is fixed as varies. Thus this expression is continuous in , and so is its finite sum . When , the empirical vectors are zero under the convention ; when , the sum is empty and is identically zero. The same continuity argument covers both cases.
Since is compact, the continuous real-valued function is bounded there. Hence some satisfies
∎Conditional averaging over the auxiliary Poisson count preserves boundedness for the threshold process used by the reported estimator.
Fix any observed sample of records from a -cell alphabet. Suppose:
(Overlap parameter.) .
(Sample size.) .
(Alphabet size.) .
The conditionally averaged threshold process of Algorithm 1, whose Poisson weights are summed over , is bounded on : there exists such that
⊢ Lean1. Continuity of the cell threshold. For , write Assign the quotient in Definition 12 the value at its zero denominator. The bounds below show that this is its continuous extension on the nonnegative cone. Since is nonnegative, implies . When , its two branches are and , according as or . On each branch, its absolute coordinate derivatives are at most ; at zero, . Comparing along the segment between two nonnegative vectors therefore gives, for , The positive-part map is -Lipschitz. Thus, for , Hence is continuous on the nonnegative cone for every fixed .
2. The pilot rectangle. Fix any pilot counts and cell . The quantities in Algorithm 1 satisfy For every and , The map is affine and continuous. Since is continuous on the nonnegative cone, its composition with this map is continuous on for every . This includes pilot counts arising when .
3. Continuity of each clipped cell estimate. Keep the counts fixed. The Jackson order and degree in Algorithm 1 satisfy and . For , set At a fixed grid point, the defining Jackson integral and the threshold formula give where cosine acts coordinatewise. The integral is finite: its argument lies in the pilot rectangle, and the integrand is continuous on a compact box. Also,
For , define the fixed tensor interpolation weights by where extracts the indicated coefficient. Tensor Lagrange interpolation of the degree- polynomial yields The preceding bounds show that every is continuous in . All count-dependent factors in are fixed and have positive radii in their denominators. Thus is continuous. Finally, is continuous, since finite minima and maxima preserve continuity.
4. Averaging and boundedness. Write for the permutations of the record positions. Conditional on the fixed sample, the average is the finite sum Only the first marks affect the count table; each marking of those retained records occurs times in the displayed sum. Thus the normalization gives the same average as markings of the retained records. The vertical bar means that the counts are computed from that permutation and marking. Each cell summand is continuous in . The capped value for is the constant zero. Hence is continuous on . Compactness of that interval gives the finite real number
∎For the lower bound, a simplex records the masses assigned to pairs of covariate cells. The paired family then isolates the effect of allocating a fixed treatment capacity across unequal benefits.
The paired causal family consists of causal completions constructed as follows. For , choose in the simplex and . For each , create cells and with masses , and set Generate the potential outcomes independently of conditional on .
⊢ LeanThe simplex in Definition 19 supplies the pair-mass vector for Definition 18.
For an integer , define
With the pair masses specified, the causal family fixes the propensity and control mean while varying the treatment mean within each pair. Treatment effects remain positive while their ranking depends on the contrast. The capacity and sampling identities make this allocation problem explicit.
Let and . The following statements hold.
(Capacity identity.) For every and every pair-mass vector and contrast vector for which satisfies the paired-completion conditions of Definition 18, the law belongs to of Definition 4. Every occupied cell has treatment effect . The half-population budget is attained by a policy satisfying For the budget values of Definition 9,
(Exact sample reduction.) For every integer , there is a Markov kernel from pairs of -record samples on the -point alphabet to observed records on the -cell alphabet with the following property. For every pair , the simplex of -point laws, set The paired law determined by belongs to . Applying the kernel to independent -record samples from and yields exactly the law of independent observed records from the observed margin of that paired law.
For two sampling laws and , the exact sample reduction gives a half-budget value of , while the full-budget value is . Thus the half-budget comparison carries a two-sample distance problem within the causal model. The statistical lower-bound input is a squared-error bound for the two-sample distance.
The following bound states the two-sample risk at the scale used by the reduction.
There is a universal constant such that, for every integer and , the minimax squared-error risk for estimating from independent observations from each of , the probability simplex on categories, satisfies
⊢ LeanWrite
We first transfer the published known- bound to this two-sample experiment. Given a two-sample estimator and a fixed , average over its second sample: Conditional Jensen inequality gives, for every , Taking the relevant suprema and infima therefore yields
The published bound (Jiao et al., 2018), applied with and , consequently supplies constants and such that For , the last condition and imply
In particular, enlarging a threshold if necessary, there is a constant such that, whenever , , , and , Indeed, gives , and the minimum is at most its second argument.
For the smaller sample sizes, use the same dense bound at the integer When , the inequalities show that , while Also , so . Applying the dense bound at thus gives, for some and threshold , If , then . An estimator with observations can use their first coordinates, whose law is exactly the -sample law. Hence
Set . To cover , consider the two parameter pairs Their targets are and . Let be the data point at which every observation in both samples has the first category, and put . The probabilities of under the two pairs are and , respectively. Thus, for every estimator , its worst-case risk satisfies since and for every real . Taking the infimum over estimators gives
Minimax risk decreases as the sample size increases by the same first-coordinate argument. Since , the preceding bound at gives
Finally, choose For , split according as or ; the sparse and dense bounds, respectively, give the claim. For , use the finite-alphabet bound. In each case the claimed minimum is at most .
∎The published intermediate-regime lower-bound input for Lemma 9 is given by Jiao et al. (2018). Combined with the exact sample reduction in Proposition 3, the lemma supplies the half-budget lower bound in Theorem 2. That bound and the upper bound in Theorem 3 yield the matched risk statement in Theorem 1 under its stated conditions.
The theorem statements and internal proofs are machine-checked in Lean 4. The sampling and causal conditions in Assumptions 1, 2, 3, and 4 are model assumptions. The published conclusion cited for Lemma 9 is a mathematical input from the literature.
Proofs of the main results
Write For a cell with , set ; its contributions below vanish. The cell masses are nonnegative, and the binary outcomes give , hence .
For an occupied cell, Assumptions 2, 3, and 4 give and For a null cell, and the same identity has both sides zero. Substituting these identities into Definition 12, and using , yields, for ,
Fix . If , then and by Definition 5. For , the inequality holds whether is nonnegative or negative. Since , Taking the maximum over feasible policies and using Definition 9 gives
For the reverse inequality, the feasible policy set is a compact subset of , contains the zero policy, and has a continuous gain. Thus a feasible maximizer exists. Applied to the affine budget and box constraints, the polyhedral normal-cone formula gives nonnegative multipliers satisfying These conditions give the hinge identity cell by cell. It is immediate when . When , a coordinate with has and ; one with has and ; an interior coordinate has both box multipliers zero and . Consequently, where the second equality uses budget complementary slackness.
If , this is a witness with price in . If , then makes every hinge at zero. Also, As , this forces . Every hinge at price is then zero as well, and the displayed witness equality holds with price . Hence in every case there is such that The process is a finite sum of continuous hinge functions on , so it is bounded there. Thus the dual infimum is well defined and is at most its value at . Together with weak duality, this proves the representation.
Finally, define Both processes are bounded on , so is finite and both dual objectives are bounded below for . For every such and every , the two inequalities give, on taking infima, Substitute the representation just proved and take the supremum over .
∎Set
Choose from Theorem 2 and from Theorem 3, and define
The discrete lower bound underlying Theorem 2 is supplied by (Jiao et al., 2018).
Fix , , and , and use the independent observed-record laws of Assumption 1. Since , evaluation of any admissible curve estimator at gives a measurable scalar estimator
By Theorem 2, there is a law for which
The middle inequality holds samplewise because belongs to the budget interval. The lower-bound result also supplies a law in the model class when applied to the zero scalar estimator, while Algorithm 1 supplies an admissible curve estimator. Thus taking the infimum over curve estimators in Definition 15 gives
For the upper bound, insert the estimator of Algorithm 1 into that infimum. Theorem 3 bounds its worst-case curve risk, so
Here , and the chosen constants satisfy .
Now let be any measurable scalar estimator. Applying Theorem 2 to the same independent observed-record laws supplies a law with , a binding half-budget policy , and
For every occupied cell, the same result gives
Finally, suppose and take any . Since and , every policy in is feasible at budget . For any such policy,
and equality is attained by the policy
Consequently, Definition 9 gives
∎Write Here ranges over measurable estimators based on observations from each of and . We first establish the two-sample bound used in the proof: for a universal .
For , this is Lemma 9. Its dense-range input is the published known- bound: when and , the worst-case squared risk is at least a positive constant times , with constants depending on (Jiao et al., 2018).
For completeness, consider the remaining range . At sufficiently large , set To obtain the finite priors used here, let Polynomial alternation gives nodes in and signed weights , normalized so that Indeed, the weights proportional to annihilate polynomials of degree at most by Lagrange interpolation; their alternating signs can be oriented to agree with the alternating approximation errors. The required approximation error has the bound For this bound, let denote the normalized Fejér kernel of order on the circle of period , and define The Fejér kernels have integral one, so . Their Fourier multipliers give when . The Fourier series of has nonnegative contributions to the magnitude of this functional; retaining the frequencies indexed from through yields Thus , which gives the displayed bound. Writing and , define The degree-zero identity makes each measure a probability measure. The remaining identities show that their moments agree through degree and that
Use cells and, for , define the two probability vectors by Under prior , the target has center . Independence gives For the stated sufficiently large alphabet threshold, . Chebyshev’s inequality therefore places at most of either prior outside the interval of radius around its center.
To compare the sample laws, Poissonize the -sample at mean . Conditional on , the two counts in pair are independent Poisson variables with means and . Relative to , their likelihood ratios obey For , define the one-pair mixture, its null reference law, its density, and the exponential scale by The likelihood identity above and the matching moments give Here because both priors are supported on . For , the factorial bound , together with , yields . Cauchy–Schwarz therefore gives The pair mixtures are independent under either prior. Telescoping their product densities and using the one-pair bound gives When a count reaches , its first marks have the fixed-sample law. For each prior, replacing the sample on the complementary event changes its predictive law in total variation by at most . The triangle inequality therefore adds twice this probability. Exponential Markov inequality at gives Since , , and , these bounds give, for the stated sufficiently large alphabet threshold, the fixed-sample predictive bound The first sample has the same law under both priors, so it leaves this comparison unchanged.
Choose the nearer of from an arbitrary estimator of . The sum of its testing errors is at least by the predictive bound. The two prior tail probabilities contribute at most ; on each remaining error event, squared estimation error is at least . Consequently for a universal . Padding the unused cell when is odd preserves the target and sample law.
The finitely many alphabet sizes below that threshold are covered by a binary comparison. Take , compare with , and set . The targets differ by , while independence and the one-record chi-squared identity give Thus their total variation is at most , and the same testing argument yields a constant multiple of . Zero-mass padding and the finite bound on give the asserted rate for these alphabet sizes. Combining the ranges, and using when , proves the displayed two-sample bound.
Now fix as in the statement. Suppose first that , and put . Then and . For each , choose the paired law of Definition 18 with The capacity and sample identities in Proposition 3 give and an exact Markov kernel taking the two independent -samples to observed records from . Apply after this kernel and condition on the two input samples. The resulting two-sample estimator of has squared risk at most times the squared risk of , by conditional Jensen’s inequality. Since the two-sample lower bound is positive, a parameter pair attains at least half its lower-bound value. Hence some paired law satisfies Pad the law with zero-mass cells to reach labels. The observed sample law, both budget values, and the occupied-cell properties are preserved; Assumption 1 identifies the stipulated sampling law with that product law.
Because and , Thus the required bound holds in this case with coefficient .
For , use one occupied pair and pad any remaining cell by zero mass. Compare paired contrasts and Both laws satisfy the class, value, occupied-effect, and binding-capacity properties by Proposition 3. Their half-budget values are and . The one-record chi-squared divergence is ; tensorization and give total variation at most for the -record laws. Testing at the midpoint of the two values then puts error probability at least under one law, on an event where absolute estimation error is at least . Therefore one of the laws satisfies For , . Taking completes both cases.
∎Fix and write Since and , we have , so . Thus, for every ,
The lower-bound input to Theorem 1 is the known-distribution minimax result of (Jiao et al., 2018). Applying the stated frontier bound and then the preceding comparison gives, uniformly over ,
The risk-bound constants can be chosen as and , respectively; they are positive, ordered, and fixed across and .
For the identity, denote the common effect in occupied cells by , so that If and , then . Cell masses satisfy and . In a zero-mass cell both sides of the following identity vanish. Hence, for every , where the last inequality is the budget constraint in Definition 5.
Define the constant policy by for every cell . Because , its coordinates are valid, and
Thus attains the upper bound. The maximization in Definition 9 equals , and therefore , as claimed.
∎1. Constants and unit bound. Write Let be the constant supplied by Theorem 4, and set Since , the inequality gives , so .
The interval is nonempty and contained in . Write The binary potential-outcome condition in Definition 4 gives , including the stated convention at empty cells. For any , the zero policy is feasible under Definition 5, and the value of every feasible policy is Hence by Definition 9. The estimator in Algorithm 1 is either or clipped to . Under Assumption 1, its squared supremum loss therefore satisfies
2. Alphabets with . In this branch, is the empirical threshold process of Algorithm 1. It is bounded on by Lemma 7. The dual representation and its uniform perturbation bound in Proposition 1, together with contraction by clipping toward , give, sample by sample,
Here is the pointwise estimate used for the empirical process. Let , index , and write for every nonnegative four-vector . For nonnegative four-vectors , define For the formula in Definition 12, explicitly define its value at the zero vector by . This is its continuous extension, since for every nonnegative with . Thus , and the stabilized arm contributions, including those of empty covariate cells, obey To see the first inequality, an arm with has ; an arm with has . When both vectors are in the latter regime, use and . When both vectors are in the first regime, . When is in the first regime and in the second, use The second term is nonnegative and . Since , its numerator satisfies Combining these inequalities cancels the coordinate in the upper bound and gives Swapping and handles the reverse case. If either total mass is zero, that vector is zero and gives the bound directly. Since is one-Lipschitz and , it follows that
Applying this cellwise and using Cauchy–Schwarz across the category-cell coordinates yields Each is the empirical mass of one observed atom. Its Bernoulli second moment under Assumption 1 gives Consequently,
Because , we have , and hence If , the unit bound above is at most . If , the displayed empirical bound is at most the same quantity.
3. Alphabets with and . Here . The estimator uses the conditionally averaged threshold process specified in Algorithm 1. It is bounded on by Lemma 8. The same dual perturbation and clipping argument bounds its curve risk by the averaged process risk:
Under the stated sampling and model conditions, Theorem 4 bounds the right-hand side by . Thus the curve risk is at most
4. Alphabets with and . Now , and Algorithm 1 sets the entire estimated curve equal to . The unit bound above gives
These cases give the claimed inequality for every , with one constant depending only on . Consider the set of expected squared losses indexed by these laws. If this set is nonempty, its supremum obeys the same bound because every member does. If it is empty, define its supremum as zero; the bound then follows from and . In the present model the set is nonempty: take uniform on , take independent of with treatment probability , and set almost surely. This law satisfies consistency and conditional exchangeability, and its treatment propensity in every cell is , as required by . Thus the nonempty case gives the stated supremum bound.
∎Write , , and . We first establish estimates for an arbitrary observed categorical law in the independent pilot and evaluation count experiment of Definition 17. All constants introduced below are positive and depend at most on , unless called numerical.
For each pilot realization, every point in the rectangle is nonnegative and satisfies . Positivity and normalization of the Jackson convolution, together with Lemma 1, therefore give the uniform bound Write the polynomial on this rectangle in tensor Chebyshev form, with coefficients : Each coefficient is a normalized tensor Chebyshev integral of the uniformly bounded path, so . If is the sum of the absolute monomial coefficients of , its recurrence gives , , and hence . Conversion to the centered monomial coefficients of Algorithm 1 now yields The estimate holds for every pilot realization, including those outside : the pilot radii are strictly positive, and the convolution rectangle lies in . Also and . Direct expansion of this last bound yields These are the two coefficient bounds required by Definition 17.
Here are the cell estimates used below. Put Conditioning on the pilot counts, factorial moments of the independent evaluation counts give On , the localization interval contains , and its radius satisfies . The second factorial-moment identity is Using , , and , it gives For each factorial index , independence of the four evaluation coordinates and the preceding moment bound give, on , Cauchy–Schwarz over the factorial indices and the coefficient envelope therefore give Here . Using gives Consequently the conditional squared bounded-variation norm is at most . Every radius is positive, so . Apply with . Uniformly in ,
To bound its approximation error, put . On , the vector lies in the pilot rectangle, so Lemma 3 gives The good-pilot inequality and the truncated endpoints imply, coordinatewise, Indeed, when , the product is at most ; the inequalities and , inserted into the formula for , give the displayed bound. When , that formula and give , so the product is at most . Since each and there are four coordinates, Thus the approximation contribution has the asserted scale, including when . Combining it with the conditional clipping contribution gives, on ,
The radius definition and truncation at zero give the pointwise estimates Taking expectations and using and yields This is the second-moment bound in Lemma 2; Cauchy–Schwarz also gives .
and for . After averaging over pilots, these inequalities convert the displayed good-pilot bound to the scale .
For the complementary pilot event, put Applying Lemma 4 with gives the weighted second-moment estimate
The pilot endpoints give and . Clipping bounds by , while Lemma 1 bounds by . Hence, on , Since , taking square roots yields, for a positive , Splitting the expectation over and , and using the preceding conditional and bad-event bounds, gives a positive such that In particular, the exponentially weighted bad-event contribution is absorbed at this scale because and is bounded for .
Define the good- and bad-pilot error paths by The pilot and evaluation counts are independent across cells. On , clipping is one-Lipschitz and cannot increase total variation. The preceding conditional factorial-moment bound, the coefficient envelope, and Lemma 1 therefore give Indeed, the clipped factorial path has squared bounded-variation norm at most a constant times ; its correction from the pilot center to has bounded-variation norm at most , since lies in the pilot rectangle. The second-moment calculation above gives . Consequently, The paths are independent across cells, continuous, and have the finite variation and second moments established above. By Lemma 5, and because , The last scale follows from and . On the branch , the inequalities and turn the last display into
For the bad-pilot paths, centering, the triangle inequality, and Cauchy–Schwarz give Here , , and . They absorb the remaining factors and give a positive with
It remains to combine the centered terms with their mean. Define The good and bad error paths partition , so the absolute value of its mean at every is at most . Since , Cauchy–Schwarz and give Applying to the centered good path, centered bad path, and mean, then using , proves
For the averaged process of Algorithm 1, define the nonnegative count-table function Its ideal expectation is finite by the preceding process bound. Conditional Jensen bounds the averaged-process risk by the capped auxiliary risk. Apply Lemma 6 to ; in the uncapped marked-Poisson experiment, is the total number of marked records, and the count-table marginal is the ideal law. Hence On , the auxiliary process is zero; implies . The Poisson cap-tail bound therefore gives The elementary bounds and show that . Hence Under Assumption 1, the product law used in this expectation is the law of the observed sample.
Choose one constant larger than every coefficient used above; for example, with the cap-transfer coefficient written , take All terms are nonnegative, so . The five estimates established for arbitrary observed categorical laws and every pilot realization give as defined in Definition 17.
Finally, take the observed margin of the full-data law from Definition 4. Summing its four observed category masses in cell gives the same covariate mass as summing the corresponding full-data masses. Moreover, Thus the common choice gives the stated -scale cell-bias and good-pilot bounds, the stated -scale bad-pilot bound, the cellwise bad-pilot envelope, and both process-risk bounds simultaneously.
∎Fix a paired completion with parameters . By Definition 18, each cell , where , has mass , treatment propensity when occupied, and weighted outcome means These identities also hold when . The paired completion satisfies consistency and conditional exchangeability. Since , its alphabet has at least two cells; since , propensity satisfies overlap on every occupied cell. Thus by Definition 4. On an occupied cell, division by gives
Summing the weighted control means and using gives Choose the policy that treats the cell when and the cell when : It selects exactly one cell per pair, including at a tie. Consequently,
To bound the value above, every and every satisfy Indeed, cell by cell, while . This bound also makes the feasible gains bounded above in the supremum defining .
For the observed margin of , the arm mass in an occupied cell is . Hence the stabilized contributions in Definition 12 equal . In a null cell all four observed masses vanish, so . To specify the quotient at this point, interpret by its zero-mass extension: for each arm . The formula in Definition 12 then gives . At , this yields Applying the preceding bound at and , and then using the feasible policy for the reverse inequality, gives Thus attains the half-population value while using treatment mass exactly .
At budget one, treating every cell is feasible. Every occupied-cell effect is positive, so no feasible policy has greater gain. The weighted treated means cancel pairwise:
For the sample reduction, fix and define as in the statement. Nonnegativity and the simplex equalities for give . If , then , so ; when the sum is zero, . Thus is an admissible contrast vector. The construction in Definition 18 supplies a paired law with these parameters. Moreover, for every , including a zero-mass pair,
Here is a kernel that depends on the input records but not on . Denote the two independent input samples by Pair their labels coordinatewise as , . Independently across coordinates, choose or with equal probability to obtain a label, choose a uniform sign , and choose an independent fair treatment indicator . Conditional on these choices, generate a Bernoulli outcome with parameter if , with parameter if and the chosen label came from , and with parameter if it came from . At , the kernel assigns probability one to the empty output sequence.
For clarity, define the Bernoulli atom mass and the two outcome parameters, for and , by The conditional mass of one output record is therefore The factors come from the three fair choices. Summing over labels, signs, treatments, and outcomes gives one, so this specifies a probability kernel.
Mixing this conditional mass over the independent input labels gives For , the second equality uses . For , it also uses and the fact that Bernoulli atom masses are affine in their parameter. The equality covers zero-mass pairs as both sides then vanish. Its right-hand side is exactly the observed atom mass of the paired law in Definition 18.
Finally, the input pairs and the kernel randomizations are independent across . Thus, for every output sequence , , the product law of observed records from that paired law. The empty product gives the same conclusion when .
∎References
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