Abstract
Because professionals sometimes do more harm than good when they intervene in the lives of other people, their policies and practices should be informed by rigorous, transparent, up-to-date evaluations. Surveys often reveal wide variations in the type and frequency of practice and policy interventions, and this evidence of collective uncertainty should prompt the humility that is a precondition for rigorous evaluation. Evaluation should begin with systematic assessment of as high a proportion as possible of existing relevant, reliable research, and then, if appropriate, additional research. Systematic, up-to-date reviews of research—such as those that the Cochrane and Campbell Collaborations endeavor to prepare and maintain—are designed to minimize the likelihood that the effects of interventions will be confused with the effects of biases and chance. Policy makers and practitioners can choose whether, and if so how, they wish their policies and practices to be informed by research. They should be clear, however, that the lives of other people will often be affected by the validity of their judgments.