Incidence - The number of new cases that occur in a defined population within a specified time period.
Mortality - The number of deaths that occur in a defined population within a specified time period.
Crude (age specific) rate - The number of new cases or deaths in a given time period divided by the population at risk. This is usually expressed as a rate per 100,000 population.
Directly Age Standardised rate - Populations can have a different age and sex structure i.e. if a population has a greater proportion of older people you would expect a greater crude rate. By applying the crude rates in sex and each age band to a standard population structure, rates for different populations can be compared. This is usually expressed as a rate per 100,000 population.
Relative Survival - An estimation of the probability of surviving from a cancer in a defined population within a specified time period. Relative survival uses the general population as a standard (100%) to give an expected number of deaths compared to the number observed. This is usually expressed as a percentage.
Survival can be presented as
a trend: different cohorts using set time point from diagnosis to see trends in survival:
a survival curve: to look at the survival of a cohort for each time period (years) from their diagnosis:
Confidence Intervals
95% confidence intervals are usually used i.e. we are 95% confident that true value lies within the specified range (or there is a 5% chance that it doesn’t). Confidence intervals are often used to compare rates in different areas or different cohorts of patients.
Further Reading:
Epidemiology for the Uninitiated, 5th ed. D Coggon, G Rose, D J P Barker.
London: BMJ Books, 2003, pp 73 ISBN 0-727-91604-1
Cancer Registration Principles and Methods, O M Jensen, D M Parkin,
IARC Sci Publ. 1991;(95)
