Measures of Disease Frequency. Nigel Paneth. FRACTIONS USED IN DESCRIBING DISEASE FREQUENCY. RATIO A fraction in which the numerator is not part of the denominator . e.g. Fetal death ratio : Fetal deaths/ live births.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
A fraction in which the numerator is not part of the denominator.
e.g. Fetal death ratio: Fetal deaths/live births.
Fetal deaths are not included among live births, by definition.
A fraction in which the numerator is part of the denominator.
e.g. Fetal death rate: Fetal deaths/all births
All births includes both live births and fetal deaths.
Ideally, a proportion in which change over time is considered, but in practice, often used interchangeably with proportion, without reference to time, (as I did previously for fetal death rate).
Divided into two types:
Proportion of individuals in a specified population at risk who have the disease of interest at a given point in time.
Proportion of individuals in a specified population at risk who have the disease of interest over a specified period of time.
(When the type of prevalence rate is not specified it is usually point prevalence, or its closest practical approximation)
Like prevalence, divided into two types:
1. Cumulative incidence rate
2. Incidence density
Number of new cases of disease occurring over a specified period of time in a population at risk at the beginning of the interval.
If we count all new cases of influenza occurring in MSU undergraduates from September 1, 1997 - August 31, 1998, and we take as the denominator all undergraduates enrolled in September 1, 1997, we would be describing the cumulative incidence rate of influenza.
Number of new cases of disease occurring over a specified period of time in a population at risk throughout the interval.
Incidence density characteristically uses as the denominator person-years at risk. (Time period can be person-months, days, or even hours, depending on the disease process being studied.)
In a STEADY STATE (i.e. if incidence is not changing, and the population is stable)
Prevalence rate = incidence rate times the duration of disease (P = I x D)