Epidemiology is the study of disease frequencies and the
causes of diseases in human populations. Terminology
from this field of study is frequently encountered in the
sports medicine literature, particularly with regard to
causes of injuries to athletes and the prevention of such
injuries. Suppose you are a team physician for a professional
football team and you noted that a relatively high
number of athletes had tears of the PCL. How common is
this problem? Two epidemiologic measures may be helpful
in understanding this problem.