Temporal stability of quality of life assessments in cancer patients.

Quality of life (QoL) is an important outcome criterion in cancer research and practice. Multiple studies have been performed to test the short-term temporal stability (1 day-2 weeks) of the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire EORTC QLQ-C30, but its stability over longer periods of time is largely unknown. The EORTC QLQ-C30 was administered at two time points between 3 and 12 months apart in six samples of cancer patients with varying characteristics (N between 298 and 923). Averaged across the six samples, the coefficients of temporal stability (intra-class correlation coefficients ICC) were between 0.31 and 0.59 for the single scales. The 2-item global health/QoL scale showed a mean coefficient of 0.44. When the stability coefficients were calculated separately for males and females and for younger vs. older patients, no systematic gender or age differences were found in the temporal stability of the QoL scales, though the stability was slightly higher in males (vs. females) and in older subgroups (vs. younger subgroups). It is nearly impossible to predict the course a cancer patients' QoL will take over a several month period. Repeated measurements are necessary to track QoL developments.