Psychometric properties of the Satisfaction With Life Scale in Parkinson's disease

The Satisfaction With Life Scale (SWLS) is a global measure of life satisfaction (LS). The objective of this study was to evaluate the psychometric properties (data completeness, scaling assumptions, targeting and reliability) of the SWLS in a sample of people with Parkinson's disease (PD).A postal survey including a Swedish version of the SWLS and demographic information was administered to 174 persons with PD; 97 responded and received a second survey after 2 weeks.The mean (SD) age and PD duration of the 97 responders were 73 (8) and 7 (6) years, respectively. Data completeness was 92% to 97% for the five items in the SWLS and 92% for the total score (5-35 points). The mean score of the SWLS was 24.2 points (7.7), indicating that this group had an average LS. The items' means and SDs were roughly parallel and the score distribution was even. The internal consistency reliability (Cronbach's alpha) was 0.90. The test-retest reliability, assessed by the intraclass correlation coefficient, was 0.78. The scale showed no systematic difference between the first and second response. The standard error of measurement was 3.6 points, and the smallest detectable difference was 10.0 points.This evaluation of the psychometric properties of the SWLS shows that the scale has good data completeness, scaling assumptions and targeting and that the internal consistency reliability and the test-retest reliability are acceptable. Thus, the SWLS is a psychometrically sound and suitable tool to asses LS in people with PD.