On assessing responsiveness of health-related quality of life instruments: guidelines for instrument evaluation.

A lack of clarity exists about the definition and adequate approach for evaluating responsiveness. An overview is presented of different categories of definitions and methods used for calculating responsiveness identified through a literature search. Twenty-five definitions and 31 measures were found. When applied to a general and a disease-specific quality of life questionnaire large variation in results was observed, partly explained by different goals of existing methods. Four major issues are considered to claim the usefulness of an evaluative health-related quality of life (HRQL) instrument. Their relation with responsiveness is discussed. The confusion about responsiveness arises mostly from a lack of distinction between cross-sectional and longitudinal validity and from a lack of distinction between responsiveness defined as the effect of treatment and responsiveness defined as the correlation of changes in the instrument with changes in other measures. All measures of what is currently called responsiveness can be looked at as measures of longitudinal validity or as measures of treatment effect. The latter ones tell us little about how well the instrument serves its purpose and are only of use in interpreting score changes. We therefore argue that the concept of responsiveness can be rejected as a separate measurement property of an evaluative instrument.