The importance of randomized field trials

This article lays out five standards for judging the importance of randomiz ed field trials in estimating the relative effects of new programs and new variations on existing programs. These standards include contemporary, eval uation policy, the historical development of trials in diverse sciences, et hics, normative practice and the credibility of alternative approaches to e stimating the effects of programs or variations. Empirical evidence and a l ine of reasoning bearing an each standard are made plain.