# Cohort Study: SIR Step 5

## SIR Step 5: Interpretation

So you know what an SIR is and can calculate one... but what does the final number actually mean?

Any SIR greater than 1.0 indicates more cases have occurred in the population than expected based on the rates of the general (or comparison) population, while an SIR less than 1.0 indicates that fewer cases have occurred.

Therefore an SIR of 21.6 or 2160% indicates that:
a. Factory employees exposed to SUPERCLEAN have more than a 20 times higher incidence rate of neurological disorder than the general population of Epiville. Answer?:
b. Factory employees exposed to SUPERCLEAN have an 80% lower incidence rate of neurological disorder than the general population of Epiville.
c. The general population of Epiville has a 20 times higher incidence rate of neurological disorder than factory employees exposed to SUPERCLEAN.
d. The general population of Epiville has an 80% lower incidence rate of neurological disorder than the factory employees exposed to SUPERCLEAN.

A bit of a warning... An SIR can be a great indicator of what is going on in your study cohort. You must, however, keep in mind the quality of your data used to compute this estimate. Like any measure used in epidemiology, the SIR is only as good as the data behind it .

[ Definition ] [ Step 1 ] [ Step 2 ] [ Step 3 ] [ Step 4 ] [ Step 5 ]