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 รท 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.
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Famous quotes containing the words period and/or prevalence:
“The post-office had a great charm at one period of our lives. When you have lived to my age, you will begin to think letters are never worth going through the rain for.”
—Jane Austen (1775–1817)
“The prevalence of suicide, without doubt, is a test of height in civilization; it means that the population is winding up its nervous and intellectual system to the utmost point of tension and that sometimes it snaps.”
—Havelock Ellis (1859–1939)