Period prevalence
Encyclopedia
In epidemiology
, Period prevalence is the proportion of the population with a given disease or condition over a specific period of time. It could describe how many people in a population had a cold over the cold season in 2006, for example.
It is expressed as a percentage of the population and can be described by the following formula:
Period prevalence (ratio) = Number of cases that occurred in a given period ÷ Number of people in the population during this period
The relationship between incidence (rate), point prevalence (ratio) and period prevalence (ratio) is easily explicated via an analogy with photography. Point prevalence is akin to a flashlit photograph: what is happening at this instant frozen in time. Period prevalence is analogous to a long exposure (seconds, rather than an instant) photograph: the number of events recorded in the photo whilst the camera shutter was open. In a movie each frame records an instant (point prevalence); by looking from frame to frame one notices new events (incident events) and can relate the number of such events to a period (number of frames) -> incidence rate.
For example....
In our street of 1000 people on 1st Jan 2011, 200 had a car. Once they have a car nobody changes their car.
Each year 365 people buy a car and 265 people get rid of one.
The point prevalence of cars in our street as at 1st Jan 2011 is 20%
The incidence of car buying is 1 per day.
The period prevalence of car ownership in 2011 is 565 or 56.5% (the number of people who, at some point in the year own a car)
The point prevalence on 1st Jan 2012 is 30% because 300 people now own a car.
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
, Period prevalence is the proportion of the population with a given disease or condition over a specific period of time. It could describe how many people in a population had a cold over the cold season in 2006, for example.
It is expressed as a percentage of the population and can be described by the following formula:
Period prevalence (ratio) = Number of cases that occurred in a given period ÷ Number of people in the population during this period
The relationship between incidence (rate), point prevalence (ratio) and period prevalence (ratio) is easily explicated via an analogy with photography. Point prevalence is akin to a flashlit photograph: what is happening at this instant frozen in time. Period prevalence is analogous to a long exposure (seconds, rather than an instant) photograph: the number of events recorded in the photo whilst the camera shutter was open. In a movie each frame records an instant (point prevalence); by looking from frame to frame one notices new events (incident events) and can relate the number of such events to a period (number of frames) -> incidence rate.
See also
- Point prevalencePoint prevalenceIn epidemiology, point prevalence is a measure of the proportion of people in a population who have a disease or condition at a particular time, such as a particular date. It is like a snap shot of the disease in time. It can be used for statistics on the occurrence of chronic diseases...
For example....
In our street of 1000 people on 1st Jan 2011, 200 had a car. Once they have a car nobody changes their car.
Each year 365 people buy a car and 265 people get rid of one.
The point prevalence of cars in our street as at 1st Jan 2011 is 20%
The incidence of car buying is 1 per day.
The period prevalence of car ownership in 2011 is 565 or 56.5% (the number of people who, at some point in the year own a car)
The point prevalence on 1st Jan 2012 is 30% because 300 people now own a car.