A Revision of the Campbellian Validity System.

The purpose of this paper is to propose a revision of the well-known Campbellian system for causal research. The revised system, termed the COPS model, applies to both applied and basic research. Five validities are included, where two validities are adopted from the Campbellian system, and the validities are partly hierarchically ordered. Important similarities and differences between the Campbellian system and the COPS model are discussed. [ABSTRACT FROM AUTHOR]