{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T21:51:32Z","timestamp":1791323492837,"version":"4.3.1"},"reference-count":68,"publisher":"Institute of Mathematical Statistics","issue":"4","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Ann. Statist."],"published-print":{"date-parts":[[2026,8,1]]},"abstract":"This paper studies the use of highly stratified designs for the efficient estimation of a large class of treatment effect parameters that arise in the analysis of experiments. By a \u201chighly stratified\u201d design, we mean experiments in which units are divided into blocks of a fixed size and a proportion within each block is assigned to a binary treatment uniformly at random. The class of parameters considered are those that can be expressed as the solution to a set of moment conditions constructed using a known function of the observed data. They include, among other things, average treatment effects, quantile treatment effects and local average treatment effects as well as the counterparts to these quantities in experiments in which the unit is itself a cluster. In this setting, we establish three results. First, we show that under a highly stratified design, the na\u00efve method of moments estimator achieves the same asymptotic variance as what could typically be attained under alternative treatment assignment mechanisms only through ex post covariate adjustment. Second, we argue that the na\u00efve method of moments estimator under a highly stratified design is asymptotically efficient by deriving a lower bound on the asymptotic variance of regular estimators of the parameter of interest in the form of a convolution theorem. In this sense, highly stratified experiments are attractive because they lead to efficient estimators of treatment effect parameters \u201cby design.\u201d Finally, we strengthen this conclusion by establishing conditions under which a \u201cfast-balancing\u201d property of highly stratified designs is in fact necessary for the na\u00efve method of moments estimator to attain the efficiency bound.<\/jats:p>","DOI":"10.1214\/26-aos2636","type":"journal-article","created":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T08:17:16Z","timestamp":1787041036000},"page":"1979-2004","source":"Crossref","is-referenced-by-count":0,"title":["On the efficiency of highly stratified experiments"],"prefix":"10.1214","volume":"54","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-1711-1220","authenticated-orcid":false,"given":"Yuehao","family":"Bai","sequence":"first","affiliation":[{"name":"Department of Economics, University of Southern California"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jizhou","family":"Liu","sequence":"additional","affiliation":[{"name":"HSBC Business School, Peking University"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Azeem M.","family":"Shaikh","sequence":"additional","affiliation":[{"name":"Department of Economics, University of Chicago"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Max","family":"Tabord-Meehan","sequence":"additional","affiliation":[{"name":"Department of Economics, University of Toronto"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"108","reference":[{"key":"22","doi-asserted-by":"publisher","unstructured":"Chen, X.<\/small>, Hong, H.<\/small> and Tarozzi, A.<\/small> (2008). 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