A review of the progress towards developing health-related quality-of-life instruments for international clinical studies and outcomes research.

This article reviews the international adaptation and use of generic health-related quality-of-life (HRQL) measures over the last several years. It focuses, as examples, on the Nottingham Health Profile (NHP), the Sickness Impact Profile (SIP), the Medical Outcomes Study Short-Form 36 Item Health Survey (MOS SF-36), the EuroQoL, Dartmouth Primary Care Cooperative Information Project (COOP) chart system, the European Organization for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire (QLQ) and the World Health Organization's WHOQOL. These instruments exemplify several different models for developing or adapting HRQL measures described in the literature, each model choosing unique approaches to the process of validation for cross-national use. There has been considerable scientific activity in recent years aimed at advancing the capabilities for international HRQL assessments. Whereas prior adaptation work was focused exclusively on translation issues, recent work has begun to rely on common methodology for translation and validation of key measurement properties across language versions. Although the major HRQL measures reviewed have not yet reached the point at which there is sufficient evidence for measurement equivalence across different language versions, internationally coordinated projects are planned and under way for these instruments to advance and refine this capacity. Preliminary evidence suggests that there are few prominent differences between countries in ranking of health states that are representative of major HRQL dimensions, and in the levels of impact of illnesses on well-being within those dimensions. Future studies should collect additional psychometric data to more fully quantify measurement equivalence among the various language versions in which each instrument is available. Additionally, more work is required to address cultural differences within nations or language groups.