Cautionary tales in the interpretation of studies of tools for predicting risk and prognosis

Assessing future risk or prognosis in individual subjects is an often difficult and humbling task for clinicians. In recent times numerous prediction tools have been developed to make the task more accurate and thereby render management decisions more appropriate. If these tools are to be used effectively, an understanding is needed of their method of development, performance characteristics, ease of use and applicability in clinical settings, and potential impact on clinical decision-making. In this fourth article in a series on critical appraisal, we discuss questions that need to be asked of any new risk prediction tool.