Assessing the clinical significance of single items relative to summated scores.

How many items are needed to measure an individual's quality of life (QOL)? This article describes the strengths and weaknesses of single items and summated scores (from multiple items) as QOL measures. We also address the use of single global measures vs multiple subindices as measures of QOL. The primary themes that recur throughout this article are the relationships between well-defined research objectives, the research setting, and the choice single item vs summated scores to measure QOL. The conceptual framework of the study, the conceptual fit with the measure, and the purpose of the assessment should all be considered when choosing a measure of QOL. No "gold standard" QOL measure can be recommended because no "one size fits all." Single items have the advantage of simplicity at the cost of detail. Multiple-item indices have the advantage of providing a complete profile of QOL component constructs at the cost of increased burden and of asking potentially irrelevant questions. The 2 types of indices are not mutually exclusive and can be used together in a single research study or in the clinical setting.