| 词条 | Prevalence |
| 释义 |
Prevalence estimates are used by epidemiologists, health care providers, government agencies, toxicologists, and insurers. Prevalence is contrasted with incidence, which is a measure of new cases arising in a population over a given period (month, year, etc.). The difference between prevalence and incidence can be summarized thus: prevalence answers "How many people have this disease right now?" or "How many people have had this disease during this time period?" and incidence answers "How many people per year newly acquire this disease?" Examples and utilityIn science, prevalence describes a proportion (typically expressed as a percentage). For example, the prevalence of obesity among American adults in 2001 was estimated by the U. S. Centers for Disease Control (CDC) at approximately 20.9%.[2] Prevalence is a term which means being widespread and it is distinct from incidence. Prevalence is a measurement of all individuals affected by the disease at a particular time, whereas incidence is a measurement of the number of new individuals who contract a disease during a particular period of time. Prevalence is a useful parameter when talking about long lasting diseases, such as HIV, but incidence is more useful when talking about diseases of short duration, such as chickenpox. {{Citation needed|date=October 2018}} UsesLifetime prevalenceLifetime prevalence (LTP) is the proportion of individuals in a population that at some point in their life (up to the time of assessment) have experienced a "case", e.g., a disease; a traumatic event; or a behavior, such as committing a crime. Often, a 12-month prevalence (or some other type of "period prevalence") is provided in conjunction with lifetime prevalence. Point prevalence is the prevalence of disorder at a specific point in time (a month or less). Lifetime morbid risk is "the proportion of a population that might become afflicted with a given disease at any point in their lifetime."[3]Period prevalencePeriod 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 existed 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 explained 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); see incidence rate. Point prevalencePoint 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. This is in contrast to period prevalence which is a measure of the proportion of people in a population who have a disease or condition over a specific period of time, say a season, or a year. Point prevalence can be described by the formula: Prevalence = Number of existing cases on a specific date ÷ Number of people in the population on this date [4]LimitationsIt can be said that a very small error applied over a very large number of individuals (that is, those who are not affected by the condition in the general population during their lifetime; for example, over 95%) produces a relevant, non-negligible number of subjects who are incorrectly classified as having the condition or any other condition which is the object of a survey study: these subjects are the so-called false positives; such reasoning applies to the 'false positive' but not the 'false negative' problem where we have an error applied over a relatively very small number of individuals to begin with (that is, those who are affected by the condition in the general population; for example, less than 5%). Hence, a very high percentage of subjects who seem to have a history of a disorder at interview are false positives for such a medical condition and apparently never suffered a fully clinical syndrome. A different but related problem in evaluating the public health significance of psychiatric conditions has been highlighted by Robert Spitzer of Columbia University: fulfillment of diagnostic criteria and the resulting diagnosis do not necessarily imply need for treatment.[5] A well-known statistical problem arises when ascertaining rates for disorders and conditions with a relatively low population prevalence or base rate. Even assuming that lay interview diagnoses are highly accurate in terms of sensitivity and specificity and their corresponding area under the ROC curve (that is, AUC, or area under the receiver operating characteristic curve), a condition with a relatively low prevalence or base-rate is bound to yield high false positive rates, which exceed false negative rates; in such a circumstance a limited positive predictive value, PPV, yields high false positive rates even in presence of a specificity which is very close to 100%.[6] See also
References1. ^{{cite book|author=Kenneth J. Rothman|title=Epidemiology: An Introduction|url=https://books.google.com/books?id=tKs7adtH-_IC&pg=PA53|date=21 June 2012|publisher=Oxford University Press|isbn=978-0-19-975455-7|page=53}} 2. ^{{cite web |url=https://www.cdc.gov/nccdphp/dnpa/obesity/trend/prev_reg.htm |title=Archived copy |accessdate=2017-09-10 |deadurl=yes |archiveurl=https://web.archive.org/web/20070519084009/http://www.cdc.gov/nccdphp/dnpa/obesity/trend/prev_reg.htm |archivedate=2007-05-19 |df= }} 3. ^{{Cite book| publisher = Oxford University Press| isbn = 978-0-19-937806-7| others = S. Charles Schulz, Michael Foster Green, Katharine J. Nelson (eds.)| title = Schizophrenia and psychotic spectrum disorders|chapter=Chapter 1: Overview of schizophrenia and treatment approaches|last1=Kruse|first1=Matthew|last2=Schulz|first2=S. Charles|page=7|location = New York|date = 2016}} 4. ^{{cite book|author=Gerstman, B.B.|year=2003|title=Epidemiology Kept Simple: An Introduction to Traditional and Modern Epidemiology (2nd ed.)|location=Hoboken, NJ|publisher=Wiley-Liss}} 5. ^{{cite journal | first = Robert | last = Spitzer | date = February 1998 | title = Diagnosis and need for treatment are not the same | journal = Archives of General Psychiatry | volume = 55 | issue = 2 | pages = 120 | url = http://archpsyc.ama-assn.org/cgi/pmidlookup?view=long&pmid=9477924 | doi = 10.1001/archpsyc.55.2.120 | pmid = 9477924 | deadurl = yes | archiveurl = http://archive.wikiwix.com/cache/20110705210403/http://archpsyc.ama-assn.org/cgi/pmidlookup?view=long&pmid=9477924 | archivedate = 2011-07-05 | df = }} 6. ^{{cite journal | first = Ross J. | last = Baldessarini |author2=Finklestein S. |author3=Arana G. W. |date=May 1983 | title =The predictive power of diagnostic tests and the effect of prevalence of illness | journal = Archives of General Psychiatry | volume = 40 | issue = 5 | pages = 569–73 |pmid=6838334 | doi=10.1001/archpsyc.1983.01790050095011}} External links{{Wiktionary|prevalence}}
3 : Epidemiology|Medical statistics|Statistical ratios |
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