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The critical element that distinguishes classical experiments from all other modes of analysis is the random assignment of treatment to enrollees in a study. This paper examines the major methodological advantages of random assignment for the purpose of estimating the effectiveness of current manpower policy. It also reviews the claimed methodological and ethical objections to experiments. The main valid objection to an experiment is neither methodological nor ethical, it is the experiment's cost in relation to that of nonexperimental methods of analysis. The authors argue that the offsetting gain from experimentation is the inherent reliability of experimental estimates of treatment effects. The paper offers a simple framework for deciding whether the improved reliability of treatment-effect estimates is worth the added cost of experimentation. It concludes with an assessment of the actual value of experiments for evaluating current manpower policies.
Burtless et al. (Wed,) studied this question.