Established in 1987, the EuroQol Group initially comprised a network of international, multilingual and multidisciplinary researchers from seven centres in Finland, the Netherlands, Norway, Sweden and the UK. Nowadays, the Group comprises researchers from Canada, Denmark, Germany, Greece, Japan, New Zealand, Slovenia, Spain, the USA and Zimbabwe. The process of shared development and local experimentation resulted in EQ-5D, a generic measure of health status that provides a simple descriptive profile and a single index value that can be used in the clinical and economic evaluation of health care and in population health surveys. Currently, EQ-5D is being widely used in different countries by clinical researchers in a variety of clinical areas. EQ-5D is also being used by eight out of the first 10 of the top 50 pharmaceutical companies listed in the annual report of Pharma Business (November/December 1999). Furthermore, EQ-5D is one of the handful of measures recommended for use in cost-effectiveness analyses by the Washington Panel on Cost Effectiveness in Health and Medicine. EQ-5D has now been translated into most major languages with the EuroQol Group closely monitoring the process.

The EuroQol five-dimensional (EQ-5D) questionnaire is used worldwide as a patient-reported outcome (PRO) instrument for the measurement and valuation of health. Several variants of the instrument now exist, including versions with three and five levels of severity and one for respondents aged 8 to 14 years. From the outset, a demand for new language versions of the EQ-5D questionnaire meant that there was a need to implement standardized procedures, which ensured that such versions were produced following international recommendations for the cultural adaptation of patient-reported outcomes. The availability of new variants and formats of the instrument, such as telephone-administered or electronic formats, complicated the task of providing and controlling the quality of cultural adaptations. Although cultural adaptations of the instrument are widely used, the procedures currently used to produce them have not been widely disseminated. The present article therefore describes the evolution of the production of other language versions of the instrument from the earliest days of simultaneous production and translation of the EQ-5D questionnaire to the more recent, broader-based strategy of version management. We describe current adaptation procedures and innovations within those procedures. We also describe how version management is organized within the EuroQol Group, review aspects related to quality control, and provide an overview of the number of currently available language versions for each variant of the EQ-5D questionnaire: three-level, five-level, and youth versions. We conclude by discussing some of the relevant issues related to cultural adaptation for frequently used instruments such as the EQ-5D questionnaire.

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