Defining clinically meaningful change in health-related quality of life.

This article reviews current approaches to defining clinically meaningful change in health-related quality of life (HRQOL) and provides guidelines for their use. Definitions of clinically meaningful change are discussed. Two broad methods for identifying clinically meaningful change are contrasted: anchor-based methods and distribution-based methods. Anchor-based methods include cross-sectional approaches and longitudinal approaches. Distribution-based methods include those based on statistical significance, sample variability, and measurement precision. Anchor-based and distribution-based methods have advantages and limitations, and neither seems to be superior to the other. An integrated system for defining clinically meaningful change is recommended that combines anchor-based and distribution-based methods. We propose a new terminology for describing meaningful change derived from anchor-based and distribution-based methods.