BACKGROUND AND OBJECTIVE: Missing data are a common problem in palliative care research. Often the most impaired patients are unable to participate in studies. This may result in biased findings. We investigated whether observed patient reported outcomes should be adjusted for bias resulting from nonparticipation. METHODS: Of 791 patients with cancer admitted to palliative care, 304 (38) participated by answering the European Organization for Research and Treatment of Cancer (EORTC) QLQ-C30 questionnaire. For the 15 symptoms and problems measured by the EORTC QLQ-C30 mean scores based on observed responses only were compared to two methods including imputed (estimated) scores based on patient characteristics for the missing data. RESULTS: All mean differences between scores based on observed responses only and the two methods including imputed scores for the missing data were less than 5 on a 0-100 scale. For 4 of the 30 comparisons a significant underestimation of symptomatology was found when using observed responses only. CONCLUSIONS: We did not find indications that using observed responses only resulted in clinically important underestimation of palliative care patients' symptomatology. Either nonparticipants' scores did not differ significantly from participants' or the variables used to describe the non-participants were insufficient predictors of the patients' scores. In any case, the study indicated that imputation of scores of nonparticipants in palliative care may not be worthwhile unless very good predictors are available.
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