Order effects: a randomised study of three major cancer-specific quality of life instruments.

BACKGROUND: In methodological studies and outcomes research, questionnaires often comprise several health-related quality of life (HRQoL) measures. Previous psychological studies have suggested that changing the sequential order of measurement scales within a questionnaire could alter the pattern of responses. Yet, information on the presence or absence of order effects on the assessment of HRQoL in cancer patients is limited. METHODS: An incomplete block design was used in this study of 1277 cancer patients. Each patient filled out a questionnaire package that contained two of the three major cancer-specific HRQoL instruments, namely the Functional Assessment of Cancer Therapy--General, the European Organization for the Research and Treatment of Cancer Core Quality of Life Questionnaire and the Functional Living Index--Cancer. Within a questionnaire package the sequential order of the instruments contained were randomised. Measurement properties of the instruments, including the number of missing values, mean HRQoL scores, known-groups validity and internal consistency were compared between samples of different presentation orders. RESULTS: No effect of presentation order on the four properties aforementioned was found. CONCLUSION: Presentation order is unlikely to alter the responses to these HRQoL instruments administered in cancer patients when any two of them are used together.