The stability of a rate is dependent on the number of events that contribute to that rate. Therefore, rates in small populations are often unstable due to the relatively small number of events that occur each year. When comparing trends over time between Middlesex-London, the province and the Peer Group, we often see a larger fluctuation in rates locally than for Ontario, in which the trends are fairly smooth from year to year – this concept needs to be considered when interpreting the time trends in this resource. Furthermore, the following strategies were implemented in order to present the most stable, reliable rates at the local level:
- Rates based on counts less than 5 have been suppressed;
- Directly age-standardized rates have only been derived where there were 20 or more events across all age groups;
- For most unadjusted rates and rates of rare outcomes, multiple years of data have been collapsed to present an average annual rate.