Psychometric and factor analytic evaluation of the 15D health-related quality of life instrument: the case of Greece

To investigate the dimensionality, construct validity in the form of factorial, convergent, discriminant, and known-groups validity, as well as scale reliability of the fifteen dimensional (15D) instrument. 15D data were collected from a large Greek general population sample (N = 3,268) which was randomly split into two halves. Data from the first sample were used to examine the distributional properties of the 15 items, as well as the factor structure adopting an exploratory approach. Data from the second sample were used to perform a confirmatory factor analysis of the 15 items, examine the goodness of fit of several measurement models, and evaluate reliability and known-groups validity of the resulting subscales, along with convergent and discriminant validity of the constructs. Exploratory factor analysis, using a distribution-free method, revealed a three-factor solution of the 15D (functional ability, physiological needs satisfaction, emotional well-being). Confirmatory factor analysis provided support for the three-factor solution but suggested that certain modifications should be made to this solution, involving freeing certain elements of the matrix of factor loadings and of the covariance matrix of measurement errors in the observed variables. Evidence of convergent validity was provided for all three factors, but discriminant validity was supported only for the emotional well-being construct. Scale reliability and known-groups validity of the resulting three subscales were satisfactory. Our results confirm the multidimensional structure of the 15D and the existence of three latent factors that cover important aspects of the health-related quality of life domain (physical and emotional functioning). The implications of our results for the validity of the 15D and suggestions for future research are outlined.