Editing Prevalence (section)

==Difference between prevalence and incidence==
{{See also|Incidence (epidemiology)#Incidence vs. prevalence}}

Prevalence is the number of disease cases ''present ''in a particular population at a given time, whereas [[incidence (epidemiology)|incidence]] is the number of new cases that ''develop ''during a specified time period.<ref>{{Cite web|url=https://www.medicinenet.com/script/main/art.asp?articlekey=11697|title=Definition of Prevalence|website=MedicineNet|language=en|access-date=2019-12-03}}</ref> Prevalence answers "How many people have this disease right now?" or "How many people have had this disease during this time period?". Incidence answers "How many people acquired the disease [during a specified time period]?". However, mathematically, prevalence is proportional to the product of the incidence and the average duration of the disease. In particular, when the prevalence is low (<10%), the relationship can be expressed as:<ref name=":0">{{Cite book |author=Bruce, Nigel |title=Quantitative methods for health research : a practical interactive guide to epidemiology and statistics|author2=Pope, Daniel |author3=Stanistreet, Debbi |date=29 November 2017|isbn=978-1-118-66526-8|edition=Second |location=Hoboken, NJ|page=16|oclc=992438133}}</ref>

:<math>Prevalence = incidence \times duration</math>

Caution must be practiced as this relationship is only applicable when the following two conditions are met: 1) prevalence is low and 2) the duration is constant (or an average can be taken).<ref name=":0" /> A general formulation requires [[differential equation]]s.<ref>{{Cite journal|language=en|author=Brinks, Ralph|title=Illness-Death Model in Chronic Disease Epidemiology: Characteristics of a Related, Differential Equation and an Inverse Problem|journal=Computational and Mathematical Methods in Medicine |year=2018 |volume=2018 |pages=1–6 |doi=10.1155/2018/5091096 |pmid=30275874 |pmc=6157110 |doi-access=free }}</ref>