Copyright 1998 by The Journal of Bone and Joint Surgery, Incorporated Current Concepts Review Principles of Epidemiology for the Orthopaedic Surgeon*

It has been stated that '"the object of any science is the accumulation of systematized verifiable knowl-edge, ' and that this is to be achieved through 'obser-vation, experiment and thought.""2 Orthopaedists are concerned primarily with individual patients; epidemi-ologists study the occurrence of disease or other health-related conditions or events in defined populations26. Epidemiological research is based on the systematic col-lection of observations related to the phenomenon of interest in a defined population. These data then are subjected to quantification, which includes the measure-ment of random variables, the estimation of population parameters, and the statistical testing of hypotheses22. The changing profile of health-care-delivery sys-tems requires orthopaedists to go beyond the individ