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This article lays out five standards for judging the importance of randomized field trials in estimating the relative effects of new programs and new variations on existing programs. These standards include contemporary evaluation policy, the historical development of trials in diverse sciences, ethics, normative practice, and the credibility of alternative approaches to estimating the effects of programs or variations. Empirical evidence and a line of reasoning bearing on each standard are made plain.
Boruch et al. (2000) studied this question.