Just one question: If one question works, why ask several?

A frequently asked question by clinical investigators is why they should use a lengthy, multi-item measurement scale to assess patients’ perceptions of their health, or quality of life, when there is evidence that a measure containing a single, global question is likely to suffice. Researchers may not wish to use lengthy scales because their core questionnaires are already long, the patient group of interest is ill or frail, they wish to minimise the burden on the patient and on the research team, or they simply want a ‘‘snap shot’’ of a topic rather than comprehensive coverage. In such circumstances, single questions have the obvious advantage of brevity, of making fewer demands than multiitem measures on respondents and researchers. Single, global questions have long been used in population surveys to measure health status, quality of life (QoL), and health related quality of life (HRQoL). The two most popular single global health items are self rated health status and self reported limiting, longstanding illness.