International development of the Quality of Life in Depression Scale (QLDS)

Abstract

Background: The Quality of Life in Depression Scale (QLDS) employs the needs-based model of quality of life (QoL) and was developed in the UK and The Netherlands as an outcome measure for clinical trials. This paper describes the production and psychometric assessment of nine new language versions for Canada (French and English), Denmark, France, Germany, Italy, Morocco, Spain and the US. Methods: Three adaptation stages were employed; production of conceptually equivalent translations, field-test interviews and assessment of reliability and construct validity by survey of patients with major depression. Results: Few problems were experienced with producing conceptually equivalent translations, except in Morocco. Patients in the field-test interviews found the instrument to have appropriate content and to be easy to complete. Internal consistency and test–retest reliability were excellent for all language versions and scores were found to relate appropriately to measures of depression severity and health status. Limitations: Further investigation is required of the ability of the measure to assess individuals at the extremes of the QoL continuum. Data collected with the Arabic QLDS should not be combined with those from other countries. Conclusions: The QLDS is the first instrument designed to assess QoL in depression based on a coherent model of the construct. Each language version has been shown to be well accepted by respondents and to have excellent psychometric properties. As the instrument is now available in a large number of languages, the QLDS is the QoL instrument of choice for inclusion in clinical trials of interventions for depression.