Indirectly Age-Standardised Rates

An excel spreadsheet template for Indirectly Standardised rates is available. 

Indirectly standardised rates compare the actual number of events in an area (e.g. South Gloucestershire) with the expected number of events based on mortality rates of a reference population (e.g. England & Wales). 

This method is often used to look at differences in mortality rates, and is often referred to as the standardised mortality ratios (SMRs).  The SMR is a ratio of observed to expected number of deaths. It can also be used to look at other events such as hospital activity. The observed figures comes from the local area, and the expected from applying the death rate in the reference population to the local population. 

Example

In this example we are comparing mortality in area A to mortality in England and Wales. The actual number of deaths in area A were 560. The following steps were used to calculate the SMR.

Step 1: Find the age-specific death rates in the reference population (England and Wales)
Step 2: Find the age-specific populations in area A
Step 3: Calculate the expected deaths in each of the age groups by multiplying the population in area A by death rate in the reference population  (England and Wales).
Step 4: Add up the number of deaths in each age group to get the total number of expected deaths. 

The table below shows the calculation of steps 1-4. 

Step 5: The SMR is the observed number of deaths /expected number of deaths expressed as a     percentage.  In this example, the SMR = (560/504)*100 = 111.