Terms used in statistics
Important concepts to understand cancer statistics
Incidence
Number of expected new cases arising in a specified population within a given period.
(e.g. 5,400 new cases)
Mortality
Number of deaths occurring in a specified population, within a given period.
(e.g. 1,600 deaths)
Both incidence and mortality can be expressed as total numbers (number of cases/deaths per year) or as rates/proportions (number of cases/deaths per 100,000 people, per year – when calculating rates it is customary to use “per 100,000 people”).
Prevalence
Prevalence is defined as the number or percent of people alive on a certain date in a population who previously had a diagnosis of the disease. It includes new (incidence) and pre-existing cases and is a function of both past incidence and survival.
Age standardized (or adjusted) rates
ASR = Age Standardized Rates
ASR is used so we can compare incidence/mortality between populations or regions that differ in respect to age. Some populations have more young people than others. This is important because age is a powerful factor in the risk of different cancers.
What ASR does is to adjust the data so we can see what it would look like if the population had a standard age structure. Once different populations are age standardized, we can compare them.
- To find age standardized incidence or mortality rates, the population data is compared with a standard population, normally the World Standard Population. The incidence or mortality rate calculated in this way is called age-standardized incidence or mortality rate and is expressed by 100,000 people.
(e.g. 60 new cases/ 100,000 people (ASR))
