Here are some definitions or explanations of specific terms and/or acronyms as they are used across the ECIS web-application.
Adjustment. A summarizing procedure applied to a statistical measure in which the effects of differences in composition of the populations being compared have been minimized by statistical methods.
Age at prevalence. Age at prevalence is the age of prevalent cases at the prevalence index date. It differs from the age at diagnosis and is the age attained by prevalent cases on the index date in which prevalence is computed.
Age-specific rate. An age-specific rate is the incidence or mortality rate for a specified age group, in which the numerator and denominator refer to the same age group; it is expressed as the number of new cancer cases or deaths per 100,000 population at risk. Five-year age categories are normally used (highest group 85+).
Age-standardised prevalence proportion. The Age-standardised (or age-adjusted) prevalence proportion is the weighted mean of all age-specific crude prevalence proportions. The weights used in the ECIS are taken from the 2013 European Standard Population. Age-standardised prevalence proportions allow comparisons over time or between populations, which are adjusted for varying age-structure of the population.
ASR (age-standardised rate). The ASR is a weighted mean of the age-specific rates where the weights are taken from the population distribution of a standard population; the ASR is expressed per 100,000. Comparison of rates referring to different time periods or different geographical areas is only possible after considering the differences in the age structure of the underlying populations. The age-standardisation allows the comparison of the rates that are arithmetically adjusted to have the same age structure of the standard population. The standard population used in the ECIS are the following 1976 European Standard Population, 2013 European Standard Population, and World Standard Population.
Crude prevalence proportion. The crude prevalence proportion (or crude proportion of prevalent cases) is the ratio of the number of prevalent cases in a specified population to the size of the population at a given date (prevalence index date). Crude prevalence proportions reflect the real burden of the disease in a population and are relevant for health care programming. Prevalence proportion is generally presented as proportion per 100,000 inhabitants or as percent proportion (%).
Crude rate. The crude rate is the ratio of the number of new cases or deaths in a specified population and time period to the size of the population at risk during the same time period. Incidence and mortality rate are usually presented as an annual rate per 100,000 persons at risk.
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.
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 rate above). The rate provides an approximation of the average risk of developing a cancer in a population for the time period of reference.
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.
Multiple primary tumours in prevalence estimations. Prevalence estimates are person-based prevalence estimates. This means that people diagnosed with multiple primary cancers are counted only once when computing estimates for all cancers combined (all sites) and, conversely, they are counted more than once when computing cancer-specific estimates, because they contribute to the prevalence counts of each primary cancer. As a consequence, the sum of all cancer-specific prevalence counts is by definition higher than the prevalence count for all cancers combined.
Percentage change. The percentage change compares two age-standardised rates (ASR): the rate of the selected country with the rate of the selected reference (Europe or EU28). The formula is (ASRcountry-ASRreference)/ ASRreference.
For example, a relative change of +5% indicates that the country rate is 5% higher than the selected reference rate. Similarly, a relative change of -10% indicates that the country rate is 10% lower than the selected reference rate.
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.
Prevalence. Prevalence is the number or proportion of people in a specified population who live after a cancer diagnosis at a certain point in time (index date).
- Limited-duration prevalence up to N years represents the number or proportion of people alive at the index date who had a diagnosis within the last N years. Limited-duration prevalence is observed by the cancer registries up to the maximum available registration time length at the index date (observed prevalence).
- Complete prevalence is the number or proportion of people alive at the index date who had a cancer diagnosis, regardless of how long before or if the patient is still under treatment or is considered cured (disease duration equal to all years from diagnosis). Complete prevalence by country in Europe was estimated in the EUROCARE-6 study applying the completeness index method to the prevalence observed by the European registries. This method consists in adjusting the registry-specific observed prevalence by a correction factor, the completeness index, which quantifies the theoretical completeness of observed prevalence as a function of the registration time length.
- Cumulative prevalence is the cumulative number or proportion of prevalent cases who had a cancer diagnosis within a specified number of years prior to the index date (0-2, 0-5, 0-10 etc).
- Interval-specific prevalence is the number or proportion of prevalent cases who had a cancer diagnosis within specified intervals of years prior to the index date (0-2, 2-5, 5-10 etc).
Prevalence in European areas. Prevalence estimates in the EUROCARE-6 study are provided by grouping countries' estimates according to the following European areas:
- NORTHERN EUROPE: Denmark, Finland, Iceland, Norway, Sweden.
- UK AND IRELAND: Ireland, UK-England, UK-Northern Ireland, UK-Scotland, UK-Wales.
- CENTRAL EUROPE: Austria, Belgium, France, Germany, Switzerland, Netherlands.
- SOUTHERN EUROPE: Croatia, Italy, Malta, Portugal, Slovenia, Spain.
- EASTERN EUROPE: Bulgaria, Czechia, Estonia, Latvia, Lithuania, Poland, Slovakia.
- EUROPEAN POOL OF REGISTRIES: all above 29 countries.
- EU-27.
Relative survival. The relative survival is a standard indicator for comparing cancer survival in population-based studies when the underlying cause of death in unknown. Relative survival is the ratio of the observed survival of patients to the expected survival in a comparable group in the general population for the same region, age, sex and calendar year. It can be interpreted as the survival probability of cancer patients in the absence of other causes of death, which can vary widely between countries. In the EUROCARE-5 study the expected survival was estimated by the Ederer II method from the lifetables of all causes mortality by age, sex, cancer registry and calendar year. Relative survival of patients diagnosed in 2000-2007 and followed up to 2008 was estimated using the classic cohort approach. Relative survival was standardised by age using the International Cancer Survival Standards (ICSS). The mean European relative survival was estimated by weighting country-specific relative survival by the country population.
Survival or Observed survival. It is the probability to survive after a given time from diagnosis (1,3, or 5-year), regardless from the cause of death. Observed survival probability is influenced by mortality due to cancer and to other causes of death. In international comparisons of cancer survival the effect of causes other than cancer, which can vary widely by countries, is removed by using relative survival.
References:
Greenland, Sander, et al. A Dictionary of Epidemiology. Vol. 6, edited by Miquel Porta, Oxford University Press, 2014.