What are anchor-based methods?
Anchor-based methods aim to establish clinically meaningful changes in a continuous outcome variable by relating or anchoring them to patient-centred measures of clinical effectiveness that could be regarded as gold standards with a high level of face validity. For example, a MID (minimum important difference) for an outcome could be defined by the minimum amount of change in that outcome necessary to make patients feel their quality of life had significantly improved. MIDs may also be based on expert clinician or consensus opinion concerning the minimum amount of change in a variable deemed to affect quality of life or health. For binary variables, any MIDs reported in the literature will inevitably be based on expert consensus, as such MIDs relate to all-or-nothing population effects rather than measurable effects on an individual, and so are not amenable to patient-centred anchor methods.