PURPOSE: General population reference data are useful in the interpretation of health-related quality of life (HRQoL) results, but for the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire C30 (EORTC QLQ-C30), such data have been published for only seven countries. In 1992, Danish general population data were collected from women only for EORTC QLQ-C30 version 1. Since no Danish reference data exists for men and women for the QLQ-C30 version 3.0, the aims of this study were to generate such data and to investigate the associations between EORTC QLQ-C30 outcomes and age, gender and morbidity, as well as trends over time.

METHODS: An age- and gender-stratified random sample of 3,080 Danes was drawn from the Danish Civil Registration System. The EORTC QLQ-C30 was administered electronically and by mail along with a short questionnaire concerning socio-demographics/morbidity.

RESULTS: Responses were obtained from 1,832 individuals (60.1 % of 3,009 eligible individuals). Response rates varied across age groups, ranging from 41.9 % (20-29 years) to 76.1 % (70-79 years). The majority of subscales were strongly associated with age and morbidity. Between genders only small, but clinically meaningful and statistically significant differences were found in five out of fifteen scales. When comparing Danish women 20 years ago and today, a tendency toward slightly improved function/reduced symptoms was observed, but the differences were small and statistically significant in only three subscales.

CONCLUSION: This study is the first to present Danish general population reference values for the EORTC QLQ-C30 version 3.0. Age and morbidity are important potential confounders that must be taken into account in HRQoL studies.