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Overview of cancer in the North West
Overview by Cancer Networks in the North West
How to get further information
Explanation of terms and their usefulness
Incidence
The incidence of a given
cancer is the number of new cases of that cancer in a defined population
during a given time period.
Mortality/Deaths
The number of patients in
a defined population who die from a given cancer during a given time period
Rates
Rates are used to compare
incidence or mortality in two areas with different sized populations. The
simplest rate is the crude rate which is the number of new cases or deaths
per 100,000 population per year.
If one wants to look at
trends in a given age group, one uses age-specific rates; for example the
numbers per 100,000 population in those aged between 55 and 64 years of age.
As cancer is more common
in the elderly, populations with a greater proportion of elderly individuals
have higher cancer rates than those made up of mainly younger people, though
the average risk of cancer may be the same in both populations. To overcome
this problem, age-standardised rates are used. One calculates a
hypothetical rate for each population assuming that both have the age
distribution of an arbitrary chosen population, which is termed the standard
population. The most common standard populations used are the European and
World standard populations; the age distribution of the actual England
population can also be used.
Survival
Survival measures how long
patients live after being diagnosed with cancer. The simplest measure is
the proportion of patients with a given cancer who are still alive at the
end of a given time period, such as one or five years after diagnosis.
Actuarial techniques are usually used in calculating such rates.
Patients with cancer
may die of other conditions. The usual way in which cancer registries take
this into account is by using relative survival rates, which are calculated
by dividing the observed survival rate by the expected survival rate for the
population under study.
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