A measure of the strength of a person’s preference for a specific health state in relation to alternative health states. The utility scale assigns numerical values on a scale of 0 (death) to 1 (optimal or ‘perfect’ health). Health states can be considered worse than death and thus have a negative value. Estimates of utility – ideally based on the use of standardised and validated generic instruments such as EQ-5D – are critical in the calculation of health-related quality of life weights used in QALYs.