Evidence
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This paper has developed a unified framework for rejective sampling, rerandomization, and regression adjustment in survey experiments, and has shown that combining these tools improves the precision of the difference-in-means estimator while preserving valid large-sample inference for the average treatment effect. Extending the asymptotic theory to more complex sampling designs and outcome models would further broaden the applicability of the proposed approach.
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Card 1 · Covariate-adjusted Fisher randomization tests for the average treatment effect
Fisher's randomization test (FRT) delivers exact $p$-values under the strong null hypothesis of no treatment effect on any units whatsoever and allows for flexible covariate adjustment to improve the power. Of interest is whether the procedure could also be valid for testing the weak null hypothesis…
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Fisher's randomization test (FRT) delivers exact $p$-values under the strong null hypothesis of no treatment effect on any units whatsoever and allows for flexible covariate adjustment to improve the power. Of interest is whether the procedure could also be valid for testing the weak null hypothesis of zero average treatment effect. Towards this end, we evaluate two general strategies for FRT with covariate-adjusted test statistics: that based on the residuals from an outcome model with only the covariates, and that based on the output from an outcome model with both the treatment and the covariates. Based on theory and simulation, we recommend using the ordinary least squares (OLS) fit of the observed outcome on the treatment, centered covariates, and their interactions for covariate adjustment, and conducting FRT with the robust $t$-value of the treatment as the test statistic. The resulting FRT is finite-sample exact for the strong null hypothesis, asymptotically valid for the weak …
Card 2 · Rerandomization in Stratified Randomized Experiments
Stratification and rerandomization are two well-known methods used in randomized experiments for balancing the baseline covariates. Renowned scholars in experimental design have recommended combining these two methods; however, limited studies have addressed the statistical properties of this combin…
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Stratification and rerandomization are two well-known methods used in randomized experiments for balancing the baseline covariates. Renowned scholars in experimental design have recommended combining these two methods; however, limited studies have addressed the statistical properties of this combination. This article proposes two rerandomization methods to be used in stratified randomized experiments, based on the overall and stratum-specific Mahalanobis distances. The first method is applicable for nearly arbitrary numbers of strata, strata sizes, and stratum-specific proportions of the treated units. The second method, which is generally more efficient than the first method, is suitable for situations in which the number of strata is fixed with their sizes tending to infinity. Under the randomization inference framework, we obtain the asymptotic distributions of estimators used in these methods and the formulas of variance reduction when compared to stratified randomization. Our ana …
Card 3 · Asymptotic Theory of Rerandomization in Treatment-Control Experiments
Although complete randomization ensures covariate balance on average, the chance for observing significant differences between treatment and control covariate distributions increases with many covariates. Rerandomization discards randomizations that do not satisfy a predetermined covariate balance c…
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Although complete randomization ensures covariate balance on average, the chance for observing significant differences between treatment and control covariate distributions increases with many covariates. Rerandomization discards randomizations that do not satisfy a predetermined covariate balance criterion, generally resulting in better covariate balance and more precise estimates of causal effects. Previous theory has derived finite sample theory for rerandomization under the assumptions of equal treatment group sizes, Gaussian covariate and outcome distributions, or additive causal effects, but not for the general sampling distribution of the difference-in-means estimator for the average causal effect. To supplement existing results, we develop asymptotic theory for rerandomization without these assumptions, which reveals a non-Gaussian asymptotic distribution for this estimator, specifically a linear combination of a Gaussian random variable and a truncated Gaussian random variable …
Card 4 · Pair-switching rerandomization
Rerandomization discards assignments with covariates unbalanced in the treatment and control groups to improve estimation and inference efficiency. However, the acceptance-rejection sampling method used in rerandomization is computationally inefficient. As a result, it is time-consuming for rerandom…
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Rerandomization discards assignments with covariates unbalanced in the treatment and control groups to improve estimation and inference efficiency. However, the acceptance-rejection sampling method used in rerandomization is computationally inefficient. As a result, it is time-consuming for rerandomization to draw numerous independent assignments, which are necessary for performing Fisher randomization tests and constructing randomization-based confidence intervals. To address this problem, we propose a pair-switching rerandomization method to draw balanced assignments efficiently. We obtain the unbiasedness and variance reduction of the difference-in-means estimator and show that the Fisher randomization tests are valid under pair-switching rerandomization. Moreover, we propose an exact approach to invert Fisher randomization tests to confidence intervals, which is faster than the existing methods. In addition, our method is applicable to both non-sequentially and sequentially randomi …
Card 5 · Randomization Tests to Assess Covariate Balance When Designing and Analyzing Matched Datasets
Causal analyses for observational studies are often complicated by covariate imbalances among treatment groups, and matching methodologies alleviate this complication by finding subsets of treatment groups that exhibit covariate balance.It is widely agreed upon that covariate balance can serve as ev…
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Causal analyses for observational studies are often complicated by covariate imbalances among treatment groups, and matching methodologies alleviate this complication by finding subsets of treatment groups that exhibit covariate balance.It is widely agreed upon that covariate balance can serve as evidence that a matched dataset approximates a randomized experiment, but what kind of experiment does a matched dataset approximate?In this work, we develop a randomization test for the hypothesis that a matched dataset approximates a particular experimental design, such as complete randomization, block randomization, or rerandomization.Our test can incorporate any experimental design, and it allows for a graphical display that puts several designs on the same univariate scale, thereby allowing researchers to pinpoint which design-if any-is most appropriate for a matched dataset.After researchers determine a plausible design, we recommend a randomizationbased approach for analyzing the matche …
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Card 3 · scope
Affected output: preserving valid large-sample inference for the average treatment effect
Model explanation: Row 3's emphasis on large-sample inference for the average causal effect under rerandomization guided the framing of the paper's contribution in the concluding synthesis.