Health-related quality of life in the general Norwegian population assessed by the European Organization for Research and Treatment of Cancer Core Quality-of-Life Questionnaire: the QLQ=C30 (+ 3).

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Abstract
PURPOSE: To obtain reference data on health-related quality of life (HRQOL) for the functional and symptom scales and single items of the European Organization for Research and Treatment of Cancer Core Quality-of-Life Questionnaire (EORTC QLQ-C30 [+ 3]) in a representative sample of the Norwegian general population. PATIENTS AND METHODS: A randomly selected sample of 3,000 people from the Norwegian population, aged 18 to 93 years, who represent geographic diversity, took part in this postal survey. The EORTC QLQ-C30 (+ 3) and a questionnaire about demographic data and health were sent by mail. A new questionnaire package was sent as a reminder after 3 weeks. RESULTS: The survey yielded a high response rate with 1,965 of 2,892 eligible persons responding (68%). There was a low amount of missing data (1.8%). Internal consistency was highly satisfactory and yielded Cronbach's alpha coefficients greater than 0.70 for all but two functional scales and one symptom scale. The sensitivity of the questionnaire was shown by the excellent discrimination between age and sex groups. Clinical validity was shown by the distinct differences according to age and sociodemographic characteristics. Women reported lower functional status and global quality of life (mean scale scores from 71.7 to 91.0) than men (mean scale scores from 75.4 to 94.4), and also more symptoms and problems. This was remarkably consistent across age groups, as was a decline in functional status with an increase in age. CONCLUSION: This is the first study that presented reference data from the EORTC QLQ-C30 (+ 3) in a sample from a general population and seems to provide valid measures of HRQOL within different age groups. The results may serve as a guideline for clinicians when interpreting HRQOL in their own groups of patients, and contributes to a better understanding of the significance of mean scores and their clinical relevance.