The clinical significance of change

Clinicians frequently make judgements about the clinical importance of a change in "score" on visual function tests obtained from patients on successive visits. Almost no normative data for assessing the significance of change in performance on routinely used clinical tests exists, and the importance of collecting such data is emphasized. A description of how normative data for the significance of change can be collected is given, using the Farnsworth-Munsell 100 hue test as an example. Although there are always limitations to estimates of error variance, the importance of determining the precision of clinical tests, for guiding rational decision making, is stressed.