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Cross-cultural validation of the Scales for Outcomes in Parkinson's Disease-Psychosocial questionnaire (SCOPA-PS) in four Latin American countries

Abstract:

Objective: To conduct a cross-national validation of the Scales for Outcomes in Parkinson's Disease-PsychoSocial questionnaire (SCOPA-PS) in four Latin American Countries. Methods: Data quality (missing items), scale assumptions (item-test correlation), internal consistency (Cronbach's alpha, item homogeneity), factor structure, content validity, and precision (standard error of measurement, SEM) of the scale were explored, as was convergent validity with motor symptoms (Clinical Impression of Severity Index [CISI-PD], Scales for Outcomes in Parkinson's Disease-Motor Scale), emotional status (Hospital Anxiety and Depression Scale) and health-related quality of life (Parkinson Disease Questionnaire-39). Known-groups validity was studied by category of severity, based on Hoehn and Yahr staging (HY), CISI-PD, and disease duration. Results: Three hundred thirty-one Parkinson's disease (PD) patients with usable data participated (mean age 64.7 years; 42.3% female; mean PD duration 8.5 years; HY, 1 to 5). Data quality (missing items <10%), scale assumptions (item-total correlation = 0.43 - 0.71) and internal consistency of SCOPA-PS (Cronbach's alpha = 0.87; item homogeneity = 0.38) were satisfactory. Factor analysis suggested a unifactorial structure. High convergent validity was found for depression (rS = 0.61), anxiety (rS = 0.62), and health-related quality of life (rS = 0.82). Known-groups validity analyses indicated a gradual influence of severity category and disease duration on SCOPA-PS scores (P < 0.0001). SEM value was 8.24 (7 to 12 in previous studies). These magnitudes may be indicative of the threshold for a real change and a minimum important difference. Conclusions: The Latin American versions of the SCOPA-PS displayed appropriate psychometric attributes. © 2008, International Society for Pharmacoeconomics and Outcomes Research (ISPOR).