Basic principles of risk score formulation in medicine.

Risk models play a vital role in monitoring health care performance. Despite extensive research and the widespread use of risk models in medicine, there are methodologic problems. We reviewed the methodology used for risk models in medicine. The findings suggest that many risk models are developed in an ad hoc manner. Important aspects such as the selection of risk factors, handling of missing values, and size of the data sample used for model development are not dealt with adequately. Methodologic details presented in publications are often sparse and unclear. Model development and validation processes are not always linked to the clinical aim of the model, which may affect their clinical validity. We make some suggestions in this review for improving methodology and reporting.