What is a rate? How precisely is it measured?
A rate is the number of events or amount of resources divided by the number in the population. For example, if an area with 100,000 enrollees has 810 hip fracture repairs, then the rate of hip fracture repair is 8.1 per 1,000 Medicare enrollees. For rare events, the rate is often re-scaled to events per 100,000 persons. Because the rates in the atlas are based on the entire Medicare population, they are for the most part precisely determined. Precision denotes the margin of error (or standard error) associated with the estimate, and is expressed as a percent of the estimated rate. Rates in larger areas and rates for more frequent events are measured more precisely. For example, for an estimated event rate of 5 per 1,000 in a median-sized HRR (N=64,000), the precision is 6%. This means that the true event rate is very likely between 4.7 and 5.3 per 1000.
