Missing forms and dropout in the TME quality of life substudy

Abstract

Missing forms may pose problems in health related quality of life (QOL) studies, because the absence of a QOL measure may be related to the patient's health and hence to the patient's QOL itself. Studying patterns of missingness, dropout, and the possible impact of missing data on QOL measures is an important step in reporting outcomes of QOL studies. We study patterns of dropout and evaluate the impact of missing forms in the TME QOL substudy. Patients with rectal cancer, randomized to receive either radiotherapy plus total mesorectal excision (TME) or TME only were included in the TME trial. QOL was evaluated in 1302 Dutch patients, before treatment, and 3, 6, 12, 18 and 24 months after surgery. Here only the visual analogue score (VAS) was studied. At baseline, differences between VAS scores were found with respect to whether the QOL forms were dated before or after radiotherapy and surgery. Differences were small between different statistical methods accounting for dropout; only a cross-sectional analysis gave biased results. The results of the sensitivity analysis indicated that a linear mixed model analysis is a reliable and attractive approach for this study.