Evaluation of the psychometric properties of the Swiss French version of the Older People's Quality of Life questionnaire (OPQOL-35-SF)

Background The proportion of the world population aged over 65 years is increasing in the world population. Quality of life is an important factor in the biopsychosocial management of older patients. The Older People's Quality of Life-35 (OPQOL-35) questionnaire was developed specifically for assessment of the quality of life of older people. The aim of this study is to evaluate the psychometric properties of a Swiss French version of the OPQOL-35 questionnaire (OPQOL-35-SF). Methods Forward-backward procedure was used to translate the original questionnaire from English into Swiss French. A sample of older people then completed the questionnaire. Construct validity of the OPQOL-35-SF was evaluated by comparing the results with those from three other questionnaires [World Health Organisation Quality of Life in older people questionnaire (WHOQOL-OLD), Control, Autonomy, Self-realization, Pleasure in 12 questions (CASP-12), and EuroQol-5-dimensions-5-levels (EQ-5D-5L)] and two visual analogue scales (health and quality of life). The structure of the OPQOL-35-SF questionnaire was assessed using exploratory and confirmatory factor analysis. To evaluate the reliability the OPQOL-35-SF questionnaire was completed a second time after 7-23 days. Results A total of 264 older people completed all the questionnaires at the first session, and 262 completed the OPQOL-35-SF again at the second session. Mean age of participants was 76.8 (standard deviation (SD) = 7.1) years. The majority of participants were women (73.9%). The Kaiser-Meyer-Olkin Measure of Sampling Adequacy (KMO) was 0.86 and Bartlett's test of sphericity was significant (p < 0.001). The result of Exploratory Factor Analysis (EFA) revealed 8 factors with eigenvalues greater than one, which explained 58% of the observed variance. All items had an acceptable loading (< 0.30) in at least one factor. The convergent validity presented low to moderate correlations (rho: 0.384-0.663). Internal consistency was good (Cronbach's alpha 0.875 for test and 0.902 for retest). Test-retest reliability presented an intra-class correlation coefficient, two-way random effects, absolute agreement, single rater (ICC2.1) of 0.83 [95% confidence interval (CI) 0.78-0.87]. Conclusions The Swiss French version of the OPQOL-35 questionnaire shows good psychometric properties, which permit its use in clinical practice or research. A supplementary sample would be necessary for a better distribution of the items in the different factors.