A brief guide to the selection of quality of life instrument.

There are numerous quality of life (QOL) scales. Because QOL experts are often partial to their own scales, researchers need to be able to select scales for themselves. Scales best suited for longitudinal purposes (clinical trials and audit) have different properties to those suited for cross-sectional studies (population and correlational studies and clinical use). The reason and logic of these differences is explained. For longitudinal use, researchers need to consider the relationship between item set, population and treatment; scales can be short, floor and ceiling effects must be avoided, and there should be extended response options. For cross-sectional use scales should have a wide range of items, should be longer, and there are no adverse floor and ceiling effects, and response options can be simpler to allow a larger set of items.