Enter the Observed Incidence and Expected Incidence into the calculator to determine the Deviation Index. This calculator can also evaluate any of the variables given the others are known.

Deviation Index Formula

The following formula is used to calculate the Deviation Index (DI).

DI = (OI - EI) / EI * 100


  • DI is the Deviation Index (%)
  • OI is the Observed Incidence (number of observed events)
  • EI is the Expected Incidence (number of expected events)

To calculate the Deviation Index, subtract the Expected Incidence from the Observed Incidence. Divide the result by the Expected Incidence, then multiply by 100 to convert the result into a percentage. This will give you the Deviation Index, which measures the difference between the observed and expected incidences as a percentage of the expected incidence.

What is a Deviation Index?

A Deviation Index is a statistical measure used to quantify the dispersion or spread of data points in a data set from the mean or expected value. It is often used in fields such as finance, economics, and data analysis to understand the variability or volatility of data. The deviation index can help identify outliers, assess risk, and understand the overall distribution and pattern of a data set.