GLOSSARY OF TERMS


Cancer Registry
The cancer registry has a pivotal role in cancer control. Its primary function is the maintenance of a file or register of all cancer cases occurring in a defined population in which the personal particulars of cancer patients and the clinical and pathological characteristics of the cancers, collected continuously and systematically from various data sources, are documented. The registry analyses and interprets such data periodically and provides information on the incidence and characteristics of specific cancers in various segments of the resident population and on temporal variations in incidence. Such information is the primary resource not only for epidemiological research on cancer determinants but also for planning and evaluating health services for the prevention, diagnosis and treatment of the disease.

Incidence
Incidence is the number of new cases arising in a given period in a specified population. This information is collected routinely by cancer registries. It can be expressed as an absolute number of cases per year or as a rate per 100,000 persons per year. The rate provides an approximation of the average risk of developing a cancer.

Population at risk
The population at risk includes all individuals susceptible to a specific cancer. It is defined on the basis of demographic variables, such as place of residence, sex, age group and (where appropriate) ethnicity.

Crude rate
Data on incidence are often presented as rates. For a specific tumour and population, a crude rate is calculated by dividing the number of new cancers observed during a given time period by the corresponding number of people in the population at risk. For cancer, the result is usually expressed as an annual rate per 100,000 persons at risk.

ASR (age-standardised rate or age-adjusted rate)
An age-standardised rate (ASR) is a summary measure; it is the rate that a population would have if it had a standard age structure. Standardization is necessary when comparing several populations that differ with respect to age structure, because age has a powerful influence on the risk of cancer. The most frequently used standard population is the World standard population. The calculated incidence rate is then called the World Standardised incidence Rate. It is also expressed per 100,000. The World standard population used in this application is as proposed by Segi (1960) and modified for the first volume of the series by Doll and al. (1996).
Age distribution of the world standard population used for age standardization in CI5
Age group World
0-4 12000
5-9 10000
10-14 9000
15-19 9000
20-24 8000
25-29 8000
30-34 6000
35-39 6000
40-44 6000
45-49 6000
50-54 5000
55-59 4000
60-64 4000
65-69 3000
70-74 2000
75-79 1000
80-84 500
85+ 500
Total 100000

Cumulative rate
Cumulative incidence is the probability of individuals getting the disease during a specified period. For cancer, it is expressed as the number of newborn children (out of 100, or 1000) who would be expected to develop a particular cancer before the age of 75 or (80 or 85) if they had the rates of cancer observed in the period, in the absence of competing causes. Like the age-standardised rate, it permits comparisons between populations of different age structures.

Standard error
The standard error of a rate is a measure of the sampling variability of the rate.