(1) The vast majority of social programs and services have not yet been rigorously evaluated, and (2) of those that have been rigorously evaluated, most (perhaps 75% or more), including those backed by expert opinion and less-rigorous studies, turn out to produce small or no effects, and, in some cases negative effects.

Even within areas where interventions do work, the differences in effectiveness are often significant. The Abdul Latif Jameel Poverty Action Lab is a network of over 100 academics who carry out rigorous impact evaluations of interventions within international development. Within a program area, they often find that the best interventions are more than ten times as effective as others with the same aim, even when excluding entirely ineffective programs.