Psychometric properties of the general self-efficacy scale in Parkinson's disease

OBJECTIVE: This study aimed to investigate the psychometric properties of the General Self-Efficacy Scale (GSE) in people with Parkinson's disease (PD). More specifically, we investigated data completeness, scaling assumptions, targeting, reliability, and construct validity.

MATERIALS AND METHODS: This study involves data available from two different projects that included people diagnosed with PD for at least 1 year, yielding two samples (1 and 2). The combined total sample (N = 346; 60% men) had a mean (SD) age and PD duration of 71 (8.9) and 9 years (6.3), respectively. Both samples received a self-administered survey by mail, which was administered twice in sample 2. Additional data (e.g., clinical assessments) were available for Sample 1.

RESULTS: Total GSE scores were computable for 336 participants (97%). Corrected item-total correlations exceeded 0.4. Principal component analyses identified one component (the eigenvalue of the first component extracted was 6.9), explaining 69% of the total variance. Floor and ceiling effects were < 6%. Internal consistency (coefficient alpha) was 0.95. Analyses of test-retest reliability yielded (ICC) values from 0.69 to 0.80. The highest value refers to those (n = 47) with identical self-ratings of mobility (in the on condition) at both tests; the standard error of measurement was 3.1 points. Construct validity was further supported by correlations in accordance with a priori expectations.

CONCLUSIONS: This study provides support for the validity and reliability of GSE scores in people with PD; the GSE can thus serve as a valuable outcome measurement in clinical practice and research.