Historically, the assessment of longitudinal construct validity in the field of psychosocial measurement involved defining hypotheses and calculating correlation coefficients using scores based on 2 measures at 2 or more time points. In the context of patient-reported outcomes, this evolved into sensitivity to change and responsiveness, including the computation of effect size estimates of change, standardized response means, and indices such as Guyatt's statistic. Cross-sectional analyses or analyses based on 2 time points have been the standard practice. Evolving conceptualizations have incorporated more than 2 time points and have included depictions of individual trajectories of change in multiple measures, structural equation models, and mixed modeling techniques. The focus of this article is on methods to evaluate longitudinal construct validity. We describe a sample of these methods and provide considerations and recommendations for designing a thoughtful longitudinal construct validity evaluation of clinical outcome assessments.
