What constitutes progress in assessing patient outcomes?

Patient self-reported disability outcomes, measured using instruments such as the Health Assessment Questionnaire Disability Index (HAQ-DI) form a foundation for clinical studies of several conditions, notably arthritis. These instruments are "static" because the instrument is the same in all applications. Although generally performing well, they may fail at extremes of disability, the so-called floor and ceiling effects. Another limitation is the degree of measurement error, the signal-to-noise ratio. These two issues drive down the statistical power of clinical trials and increase their expense.