The Principle of Proximal Similarity

Abstract

This comment focuses on Campbell's principle of proximal similarity. When considered in the light of related work in various disciplines, the principle has implications that go beyond the generalization of experimental results in preventive intervention research. The generalized principle suggests classification and conceptualization of the settings and people involved in preventive interventive research in terms offuzzy-boundary categories, in contrast to conventional classical or sharp-boundary categories. As such, the generalized principle raises opportunities (1) to use systematic, empirical methods for purposive sampling and other tasks in problem-oriented research, (2) to reconsider the epistemological foundations that shape such research, including the concept of 'science,' and (3) to include subjects with scientists in the mutually reinforcing community that is expected to evolve effective treatments. The principle is applicable to policy research in general.