# Comparison of two rates

Command: | Tests Rates Comparison of two rates |

## Description

A rate is a ratio between a count and another measurement, for example the ratio of a number of events observed and the total number of person-years of observation.

This procedure allows to compare the rates in two groups.

This test is not performed on data in the spreadsheet, but on data you enter in a dialog box.

## Required input

**Numerator**: the observed number of events in each group.**Denominator**: for example the total person-years for each group.- Option
**Express result as 1:X**: when this option is selected the rate R will be displayed as 1:(1/R), e.g. the rate 10/200 equals 0.05 and can be represented as 1:20.

When all data have been entered click the Test button.

## Results

The program displays:

- The (incidence) rate in the two groups with their Poisson 95% Confidence Interval.
- The difference between the two rates R2-R1 with its 95% Confidence Interval and associated P-value. If the P-value is less than 0.05 it can be concluded that there is a statistical significant difference between the two rates.
- The ratio of the two rates R1/R2 and its 95% Confidence Interval. If the value 1 is not in this interval, it can be concluded that the ratio R1/R2 is not significantly different from 1 (in which case the rates would be equal).

In the *Comment* input field you can enter a comment or conclusion that will be included on the printed report.

## Literature

- Sahai H, Khurshid A (1996) Statistics in epidemiology: methods, techniques, and applications. Boca Raton, FL: CRC Press, Inc.