GLOSSARY OF TERMS

Mortality
Mortality is the number of deaths occurring in a given period in a specified population. It can be expressed as an absolute number of deaths per year or as a rate per 100,000 persons per year.


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. Years of risk duration are counted in person-years. 


Age-specific rate
The age-specific rate is calculated simply by dividing the number of cancer deaths observed in a given age category during a given time period by the corresponding number of person years in the population at risk in the same age category and time period. For cancer, the result is usually expressed as an annual rate per 100,000 person-years.


Crude rate
Data on mortality are often presented as rates. For a specific tumour and population, a crude rate is calculated simply by dividing the number of cancer deaths observed during a given time period by the corresponding number of person years 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)
An age-standardised rate (ASR) is a summary measure of 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 because age has a powerful influence on the risk of dying from cancer. The ASR is a weighted mean of the age-specific rates; the weights are taken from population distribution of the standard population. The most frequently used standard population is the World Standard Population. The calculated mortality rate is then called age-standardised mortality rate (world). The world standard population used within the application is as proposed by Segi (1960) and modified by Doll and al. (1996). The ASR is also expressed per 100,000.

Age distribution of the world standard population
Age group wi
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 risk
Cumulative mortality is the probability or risk of individuals dying from the disease during a specified period. For cancer, it is expressed as the number of new born children (out of 100, or 1000) who would be expected to die from 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.


Confidence interval
A range of values that has a specified probability of containing the unknown true rate or trend. The 95% (p-value = .05) and 99% (p-value = .01) confidence intervals are the most commonly used.


Annual percentage change (APC)
The annual percentage change is used to describe the magnitude of change in the trend on fitting a simple regression model to the log of the ASR. It is the average annual rate of change in the ASR over the time period selected.

References
  1. Segi, M. (1960) Cancer Mortality for Selected Sites in 24 Countries (195057). Department of Public Health, Tohoku University of Medicine, Sendai, Japan.
  2. Doll, R., Payne, P., Waterhouse, J.A.H. eds (1966). Cancer Incidence in Five Continents, Vol. I. Union Internationale Contre le Cancer, Geneva.

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