The EuroQol Five Dimension (EQ-5D) is an example of a generic measurement of quality of life, which is used in many clinical trials and other prospective studies. The EQ-5D questionnaire consists of five questions relating to different domains of quality of life: mobility, self-care, usual activities, pain/discomfort, anxiety/depression. For each of these domains there are three levels of response: no problems, some problems or severe problems. More recently, questions with five levels of response have been introduced (called EQ-5D-5L). The instrument is quick and easy to use, extensively researched/validated and translated into many different languages. Most importantly, it is not disease-specific and therefore applicable to most disease areas and comparisons of interventions across disease areas. However, it less applicable in mental health and diseases causing specific disabilities such as blindness.

The importance of EQ-5D is that based on population surveys, utility scores are available for each of the possible responses. These can be combined with appropriate durations for each measurement to generate quality-adjusted life years for each study subject, which then can be used to drive cost-utility analyses of the intervention of interest. It is generally recommended that in clinical trials EQ-5D is administered alongside a disease specific quality of life instrument which is more sensitive to specific aspects of the condition and the potential impact of therapy. NICE guidelines state that the EQ-5D is the preferred measure of HRQL in adults, and ‘when EQ-5D data are not available or are inappropriate for the condition or effects of treatment, the valuation methods should be fully described and comparable to those used for the EQ-5D’.