A sample has value when it provides actionable in-
formation about the populationof interest. The entire
population consists of measurements on all units of in-
terest to the study, but complete enumeration of the en-
tire population of units is unlikely to be accessible for
cost or logistical reasons. This of course is not true when
a medical practice uses a fully electronic record. We se-lect a subset or sample of the population so that we may
obtain sufficient information to address the problem we
are trying to solve [5]. A statistical power analysis or
other method is used to calculate, under various assump-tions, the needed sample size.