The clinical impression of severity index for Parkinson's disease: International validation study

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Abstract
This study sought to provide further information about the psychometric properties of the Clinical Impression of Severity Index for Parkinson's Disease (CISI‐PD), in a large, international, cross‐culturally diverse sample. Six hundred and fourteen patients with PD participated in the study. Apart from the CISI‐PD, assessments were based on Hoehn & Yahr (HY) staging, the Scales for Outcomes in PD‐Motor (SCOPA‐M), ‐Cognition (SCOPA‐COG) and ‐Psychosocial (SCOPA‐PS), the Cumulative Illness Rating Scale‐Geriatrics, and the Hospital Anxiety and Depression Scale. The total CISI‐PD score displayed no floor or ceiling effects. Internal consistency was 0.81, the test–retest intraclass correlation coefficient was 0.84, and item homogeneity was 0.52. Exploratory and confirmatory factor analysis (CFI = 0.99, RMSEA = 0.07) confirmed CISI‐PD's unifactorial structure. The CISI‐PD showed adequate convergent validity with SCOPA‐COG and SCOPA‐M (rS = 0.46–0.85, respectively) and discriminative validity for HY stages and disease duration (P < 0.0001). In a multiple regression model, main CISI‐PD predictors were SCOPA‐M, disease duration, and depression. The results obtained were not only comparable to but also extended those yielded by the preliminary validation study, thus showing that the CISI‐PD is a valid instrument to measure clinical impression of severity in PD. Its simplicity and easy application make it an attractive and useful tool for clinical practice and research.