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 multi-item 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.

SELF RATED HEALTH STATUS

The classic self rated health status item consists of asking respondents to rate their health as “excellent, good, fair, or poor”. Variations of this question have been used in surveys worldwide. Literature reviews on the conceptualisation and measurement of health published by Rand in the USA^1,2 and an overview by Stewart and Ware³ reported citations of the self rated health item as early as early as the 1950s. For example, a version appeared in a US study of occupational retirement⁴ and in the US Federal Civil Defense Administration Survey, both in the 1950s.⁵ And a question asking people to rate their general health, followed …