Quality of Life in Depression Scale (QLDS): Adaptation and evaluation of the psychometric properties of the Norwegian version

Abstract

Despite the prevalence of depression, few studies on the quality of life of depressed patients have been conducted. The Quality of Life in Depression Scale (QLDS) is the first depression-specific measure. Since its publication in 1992, the measure has been adapted and re-validated for use in several countries. This paper describes the adaptation and psychometric evaluation of the Norwegian version of the QLDS. The QLDS was translated into Norwegian by means of bilingual and lay translation panels. Face and content validity was assessed, and a validation study was conducted with 72 depressed patients in order to establish the new adaptation's internal consistency, reproducibility, construct validity and responsiveness. No major problems were experienced during the translation of the QLDS into Norwegian and patient interviews indicated that the questionnaire was both acceptable to and relevant for depressed patients. The validation/adaptation of the QLDS into Norwegian had been successful. High test–retest correlations indicated excellent reproducibility with no evidence of excessive random measurement error. The internal consistency of the measure was confirmed, with items adequately inter-related. Evidence of construct validity and responsiveness is also encouraging. The Norwegian QLDS is a reliable and valid measure of quality of life.