VALIDATION OF THE EORTC QLQ-C30 QUALITY-OF-LIFE QUESTIONNAIRE THROUGHCOMBINED QUALITATIVE AND QUANTITATIVE ASSESSMENT OF PATIENT-OBSERVER AGREEMENT

Patient-rated questionnaires are increasingly used to assess health-re lated quality of life. We studied one aspect of the validity of such m easures that has rarely been investigated: do patients interpret quest ionnaires in the same way as do the researchers reporting the results? If not, there may be a problem. We employed the EORTC QLQ-C30 quality -of life questionnaire to study 95 cancer patients anti measured the a greement. between (1) the patient's self assessment and (2) an observe rs rating of the patient's open-ended responses to the same questionna ire administered as an interview. The observer made qualitative record ings describing potential misinterpretations. The agreement between pa tients' and observers' ratings was high (median kappa = 0.85, range 0. 49-1.00). The qualitative data revealed a few minor validity problems. One of these, selective reporting, may lead to systematic errors: som e patients reported only what they considered ''relevant'' symptoms. T he combination of quantitative and qualitative methods proved useful f or questionnaire validation. (C) 1997 Elsevier Science Inc.