Need for standardization in population-based quality of life studies: a review of the current literature.

In this systematic review we focus on the current use of and knowledge on health related quality of life in unselected, population-based IBD cohorts. We made a systematic literature search and included for comprehensive review papers that described a population-based cohort and that used validated HRQoL instruments. We show that even studies defined by the authors as population-based do not always meet the criteria set for being population-based. The heterogeneity of the study populations we have reviewed emphasizes that "population-based" must be defined very meticulously and that study populations need to be scrutinized with regard to all characteristics of the cohort before one can compare their results. Different definitions of study populations as population-based affect outcomes. We also show that use of the same HRQoL questionnaires does not guarantee comparable results as there are several different versions of the questionnaires, the different translations are not always comparable and at last there are several methods of computing and presenting the data. Detailed accumulation of knowledge and thorough meta analyses is therefore difficult hence we find it necessary to raise a discussion on the need of standardization in this field of research and we make some simple recommendations on factors we find important.