[Measuring quality of life: as simple as possible and as detailed as necessary].

Numerous instruments for measuring health-related quality of life have been developed over the past decades. Explicit methodological criteria should be used to select an instrument to use in a given study. Based on a list of such methodological criteria, this paper provides guidance for choosing appropriate quality of life instruments. Special emphasis will be given to the advantages and disadvantages of using generic and disease-specific instruments as these are the main types of quality of life measures. Finally, the development and the use of short forms of existing instruments will be discussed.