Rate (epidemiology)

A rate is in the epidemiology a measure of frequency of an event in a specific population (population) occurs in a defined time period. The use of rates rather than raw numbers is essential for comparing experiences between populations at different times, in different places, or between different groups of people.

definition

The components of a rate are the numerator, denominator, the specified length of time that events occur, and usually a multiplier, a power of 10, that converts the rate from a hard-to-use fraction or decimal to an integer. In epidemiology, the denominator is given by the mean population at risk or the person time at risk. In epidemiology, a rate is given by: ${\displaystyle \Delta t=[t_{0},t_{1}]}$

${\displaystyle {\text{Rate}}={\frac {{\text{Anzahl der Ereignisse innerhalb einer bestimmten Zeitspanne}}\;\Delta t}{\text{mittlere Populationsgröße im gleichen Beobachtungszeitraum}}}\times 10^{n}}$.

Alternatively, in epidemiology, the person time at risk is often used in the denominator, i.e. the period of time added up over all persons in which the persons are actually at risk of developing the disease and can be observed.

If one chooses the number of incidence cases (the number of new patients) for the numerator in the above definition, one speaks of an incidence rate .

Terminology in Epidemiology

Especially in English-language textbooks on epidemiology, measures whose designation includes the addition “rate” are often not defined as the ideal word usage of a rate. The addition “rate” serves as a surrogate for the terms cumulative incidence or proportion (such as the infestation rate and the proportion of cases / deaths) and is often not limited to ratios that represent changes over time . According to this ideal usage of a rate, the lethality “rate” would not be a rate in the strict sense of the word . Instead, the Robert Koch Institute suggests the term deceased percentage . If one were to define the mortality rate according to the ideal usage of a rate, then one would divide the number of people who died within a period by the mean population size (over the same period).

In contrast, the hazard rate is truly a rate because it can be expressed as the number of cases that develop per unit of time divided by the total size of the population at risk.

Individual evidence

1. ↑ Wolfgang Kiehl: Infection protection and infection epidemiology. Technical terms - definitions - interpretations. Ed .: Robert Koch Institute, Berlin 2015, ISBN 978-3-89606-258-1 , p. 108, keyword rate .
2. ↑ John M. Last: A Dictionary of Epidemiology. , 4th edition, 2001 International Epidemiological Association , Oxford UP 2001, p. 151. Keyword: Rate .
3. ↑ John M. Last: A Dictionary of Epidemiology. , 4th edition, 2001 International Epidemiological Association , Oxford UP 2001, p. 151. Keyword: Rate .
4. ↑ John M. Last: A Dictionary of Epidemiology. , 4th edition, 2001 International Epidemiological Association , Oxford UP 2001, p. 151. Keyword: Rate .
5. ↑ SARS-CoV-2 fact sheet on Coronavirus-Disease-2019 (COVID-19). Retrieved August 17, 2020 . 
6. ↑ GBE glossary. In: Robert Koch Institute . Keyword: lethality, lethality rate .