Case sampling for psychotherapy practice, theory, and policy guidance: Qualities and quantities

Area of Science:

• Psychology
• Clinical Psychology
• Research Methodology

Background:

• Random sampling is often impractical in psychotherapy research.
• Opportunistic and purposive sampling are commonly used alternatives.

Purpose of the Study:

• To analyze the implications of non-random sampling in psychotherapy research.
• To determine the extent to which findings from such studies can be generalized.
• To assess the utility of current research methods for theory development and practice.

Main Methods:

• Focus on two-phase cross-sectional input-outcome studies, a common format in psychotherapy outcome research.
• Analysis of sampling strategies in relation to independent and dependent variables.
• Examining the generalizability of associations found through non-random sampling.

Main Results:

• Non-random sampling (opportunistic, purposive) precludes generalization of population-distribution statistics.
• However, it supports the reporting of associations between independent and dependent variables.
• These identified associations can be generalized to the sampled population with a certain frequency.

Conclusions:

• While broad statistical generalizations are limited, non-random sampling in psychotherapy research is sufficient for suggesting and testing theories.
• Findings can inform psychotherapy practice by highlighting specific variable associations.
• Two-phase cross-sectional studies remain a feasible and valuable approach for psychotherapy outcome research.