Essays in Social Experimentation: What Experiments are Needed for Manpower Policy?

Experiments, where prospective participants are randomly assigned into experimental and control groups, are often regarded as the ideal approach to evaluation of manpower policies. This examination shows that such experimental designs can yield misleading and incomplete information about program impacts in cases where program effects vary among individuals. When individual heterogeneity is present, such designs at best provide unbiased estimates of average program effects, not of marginal effects. The latter are often more important for policy than the former. This paper proposes alternative experimental designs that permit estimation of the marginal as well as average program impacts.