[Excerpt] Society has limited resources and many competing uses for them. I therefore take it as being an almost obvious proposition that at any point in time policy makers should strive to maximize the social benefits produced by the available funds they have to spend. This proposition implies that evaluation research should be undertaken either by or for government agencies. Policy makers need to know what benefits are being produced by each social program and the resource costs involved. They need to know which aspects of which programs are working and which programs need to be replaced.