Longitudinal psychometric attributes, responsiveness, and importance of change: An approach using the SCOPA‐Psychosocial questionnaire

Abstract

The objective of this study was to illustrate the analysis of longitudinal validity, responsiveness, and importance of change, using the SCOPA-Psychosocial Questionnaire (SCOPA-PS) as a source of empirical data. Sixty-seven patients with PD in Hoehn and Yahr (HY) stage 2 were followed up for 1 year and assessed by means of the Schwab and England Scale, Unified PD Rating Scale (UPDRS), Hospital Anxiety and Depression Scale (HADS), PDQ-39, and SCOPA-PS. A range of methods was applied to enable each of the target attributes to be analyzed from different conceptual stances. The SCOPA-PS displayed satisfactory acceptability (no floor or ceiling effect), internal consistency (alpha = 0.80-0.84), convergent validity (r(S) = 0.70-0.82 with PDQ-39), and precision (SEM = 8.80), both at baseline and at the end of follow-up. The threshold value for significant change ranged from 17.25 (1.96 SEM) to 24.39 (Smallest real difference and Reliable change index). Threshold values for a clinically meaningful change were 0.73-1.26 (effect size, standardized response mean, responsiveness statistic). Change in SCOPA-PS scores correlated strongly with change in total UPDRS, HADS, and PDQ-39 scores, and reliably detected 70% of cases that worsened according to the PDQ-39. The minimally important change (MIC) for "minimally impaired" patients as per the PDQ39 was 8.30-9.10 points. Indices such as 1.96 SEM, effect size, and correlation with the change in other measures provide useful information about different concepts of responsiveness. The MIC should be determined for each specific setting, using distribution- and anchor-based methods. The SCOPA-PS showed satisfactory longitudinal attributes and responsiveness in stage-2 Brazilian patients with PD across 1 year of follow-up.