The incorporation of patient-reported health-related quality of life (HRQL) measures to better assess clinical outcomes has been an important goal of evidence-based medicine (Guyatt et al. 1997). The Medical Outcomes Study Short-Form 36-Item Health Survey, or SF-36, is the most widely used HRQL instrument in the world (Brazier, Harper, and Jones 1992). Designed as a generic instrument capable of measuring the HRQL of individuals with different diseases or health conditions, the SF-36 yields scale scores for eight domains: Physical Functioning, Role Physical, Bodily Pain, General Health, Vitality, Social Functioning, Role Emotional, and Mental Health. Recently, this instrument was revised to reflect improved wording and response options, and Version 2 is now available for patient reported measurement of HRQL outcomes (Ware, Kosinski, and Dewey 2000).

Other HRQL measures, primarily disease-specific instruments designed to measure particular health conditions, have established standards for determining clinically important differences (CIDs) using various approaches for interpreting important changes over time (Guyatt et al. 2002). Many consumers seek such standards or thresholds for interpreting and evaluating change on these important outcomes (Symonds et al. 2002). These consumers include not only patients, clinicians, and clinical researchers but also pharmaceutical and medical device manufacturers who must demonstrate the usefulness of their products, and government regulators who, along with insurance payers, must evaluate the usefulness and consequences of each product seeking endorsement or coverage. Without established standards for interpreting the change in HRQL measures attributed to treatments or interventions, these consumers must often resort to statistical evaluations that rely on the variation in a sample(s) and the number of enrollees or power to detect a statistically significant difference (p< .05) between two groups, such as treatment versus placebo. Statistically significant differences, however, do not imply that a meaningful or relevant difference has been demonstrated for the individuals enrolled in such trials (Sloan et al. 2002).