# Glossary of Terms

Here are some definitions of specific terminology and/or acronyms you may see when browsing the EUREG website. Please contact IARC if you have more detailed questions about a term that may or may not exist on this page.

## List of definitions

### 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 (see age-specific rate and ASR below). The rate provides an approximation of the average risk of developing a cancer.

### 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.

### Survival

It is defined as the probability of survival, expressed as time elapsed since diagnosis (1,3 5-year survival). This observed survival probability is influenced by mortality both from cancer of interest and from other causes. For this reason, relative survival is usually calculated. It is defined as the ratio of the observed survival in the group of patients to the survival expected in a group of people in the general population, who are similar to the patients with respect to all possible factors affecting survival at the beginning of the follow-up period, except for the disease of interest.

### Population at risk

The part of a population which is susceptible to develop a specific cancer. It is defined on the basis of demographic data, such as place of residence, sex, age group, etc. Years of risk duration are counted in person-years.

### Age-specific rate

The age-specific rate is calculated simply by dividing the number of new cancers or 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. In EUREG, five-year age categories are used (highest group 85+).

Age distributions of the standard populations used for age standardisation in EUREG | ||
---|---|---|

Age group | World w_{i} |
European w_{i} |

0-4 | 12000 | 8000 |

5-9 | 10000 | 7000 |

10-14 | 9000 | 7000 |

15-19 | 9000 | 7000 |

20-24 | 8000 | 7000 |

25-29 | 8000 | 7000 |

30-34 | 6000 | 7000 |

35-39 | 6000 | 7000 |

40-44 | 6000 | 7000 |

45-49 | 6000 | 7000 |

50-54 | 5000 | 7000 |

55-59 | 4000 | 6000 |

60-64 | 4000 | 5000 |

65-69 | 3000 | 4000 |

70-74 | 2000 | 3000 |

75-79 | 1000 | 2000 |

80-84 | 500 | 1000 |

85+ | 500 | 1000 |

Total | 100000 | 100000 |

### Crude rate

Data on incidence or mortality are often presented as rates. For a specific tumour and population, a crude rate is calculated simply by dividing the number of new cancers or 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 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 incidence or mortality rate is then called age-standardised incidence or mortality rate (world). It is also expressed per 100000. The European standard is often used and EUREG gives the possibility of also choosing this standard.

### Cumulative risk

Cumulative incidence/mortality is the probability or risk of individuals getting/dying from the disease over a specified age-span. Cumulative risk is expressed as the number of cases/deaths per 1000 person-years that are expected to occur in a given population between the specified age limits (e.g. between birth and the age 84 years) if the cancer rates were as those observed in the specified time period in the absence of competing causes. Like the age standardised rate, Cumulative risk permits comparing between populations of different age structures.

In EUREG selecting the age range 0-85+ or 0-84 will return Cumulative risk for the age-range 0-84; selecting the age range 35-64 will return Cumulative risk for the age-range 35-64, etc. If the last age group available is 0-84+ (see EUREG database table of registries) and the entire life-span is selected, Cumulative risk for the age-range 0-79 is returned.

### 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. It is the average annual rate of change in the ASR over the time period selected.
It is calculated by fitting a regression line to the natural logarithm of the rates
or of the number of cases or deaths using calendar year as a regressor variable,
i.e. y = mx + b where y = ln (rate) and x = calendar year. Then the APC = 100*(e^{m}
-1).

### Overall percentage change (OPC)

OPC = (1+APC)^{number of years} -1