Change process research (CPR) is the study of the processes by which change occurs in psychotherapy, and is a necessary complement to randomized clinical trials and other forms of efficacy research. In this article I describe and evaluate of four types of CPR. The first three are basic designs and include quantitative Process-Outcome, qualitative Helpful Factors, and micro-analytic Sequential Process; the fourth, the Significant Events approach, refers to methods such as Task Analysis and Comprehensive Process Analysis that integrate the first three. The strengths and weaknesses of each design are described and summarized using both causal and practical criteria, as part of an overall argument for systematic methodological pluralism
