In epidemiology, the prevalence of a health-related state (typically disease, but also other things like smoking or seatbelt use) in a statistical population is defined as the total number of cases of the risk factor in the population at a given time, or the total number of cases in the population, divided by the number of individuals in the population. It is used as an estimate of how common a disease is within a population over a certain period of time. It helps physicians or other health professionals understand the probability of certain diagnoses and is routinely used by epidemiologists, health care providers, government agencies and insurers.

Suppose we define a as the number of individuals in a given population with the disease at a given time, and b as the number of individuals in the same population at risk of developing the disease at a given time, not including those already with the disease. Then, we can write the prevalence as

Failed to parse (Missing texvc executable; please see math/README to configure.): \mbox{prevalence} = \frac{a}{a + b}

Prevalence may also be expressed in terms of subgroups of the population based on different denominator data.

Prevalence is contrasted with incidence which is a measure of new cases.

Examples and utility[link]

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%. In plain English, "prevalence" simply means "extent", but in scientific English it means "proportion" (typically expressed as a percentage) .

Prevalence is distinct from incidence. Prevalence is a measurement of all individuals affected by the disease within a particular period of time, whereas incidence is a measurement of the number of new individuals who contract a disease during a particular period of time.

To illustrate, a long term disease that was spread widely in a community in 2002 will have a high prevalence at a given point of 2003 (assuming it has a long duration) but it might have a low incidence rate during 2003 (i.e. lots of existing cases, but not many new ones in that year). Conversely, a disease that is easily transmitted but has a short duration might spread widely during 2002 but is likely to have a low prevalence at any given point in 2003 (due to its short duration) but a high incidence during 2002 (as many people develop the disease). As such, 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.

Lifetime prevalence (LTP) is the number of individuals in a statistical population that at some point in their life (up to the time of assessment) have experienced a "case" (e.g., a disorder), compared to the total number of individuals (i.e. it is expressed as a ratio or percentage). Often, a 12-month prevalence (or some other type of "period prevalence") is used in conjunction with lifetime prevalence. There is also point prevalence, the prevalence of disorder at a more specific (a month or less) point in time. There is also a related figure lifetime morbid risk - the theoretical prevalence at any point in life for anyone, regardless of time of assessment. (example: Synopsis of article on "How Prevalent Is Schizophrenia?" from Public Library of Science)

Limitations[link]

It 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.^[1]

See also[link]

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%.^[2]

Look up prevalence in Wiktionary, the free dictionary.

• Incidence
• Rare disease
• Denominator data

References[link]

External links[link]

• PlusNews, the UN's HIV/AIDS news service provides HIV prevalence rates for nearly 60 countries worldwide

Giovanni Sollima (born 24 October 1962 in Palermo, Sicily, Italy) is an Italian composer and cellist. He was born into a family of musicians and studied cello with Giovanni Perriera and composition with his father, Eliodoro Sollima, at the Conservatorio di Palermo, where he graduated with highest honors. He later studied with Antonio Janigro and Milko Kelemen at the Musikhochschule Stuttgart and at the Universität Mozarteum Salzburg.

As a composer, Sollima's influences are wide ranging, taking in jazz and rock, as well as various ethnic traditions from the Mediterranean area.^[1] Sollima's music is influenced by minimalism, with his compositions often featuring modal melodies and repetitive structures. Because his works are characterized by a more diverse and eclectic approach to material than the early American minimalist composers, the American critic Kyle Gann has called Sollima a postminimalist composer.^[2]

Sollima has collaborated with the American poet and musician Patti Smith, appearing on her records and performing with her in concert. He also collaborates with the Silk Road Project.

Music for chamber ensembles[link]

Orchestral works[link]

Opera and ballet[link]

• Notti di Grazia (1991) - Melodramma in un atto, libretto by Dario Oliveri
• Mittersill 101 variazioni sul caso Anton Webern (1996) - Video opera, text by Dario Oliveri, after Goethe
• Cenerentola Azzurro (1994) - Text by Dario Oliveri
• Casanova (2000) - Choreography by Karole Armitage
• Matteo Ricci — Li Madou (2001) - Melologue, text by Filippo Mignini
• J. Beuys song (2001) - Choreography by Carolyn Carlson
• Ellis Island (2002) - Opera in 2 acts, libretto by Roberto Alajmo

Incidental music for the theatre[link]

• Match (1990)
• Cordelia & co. (1991)
• 3 pezzi for " Il sogno spezzato di Rita Atria" (1993)
• 3 pezzi for "Pippo Fava" (1994)
• I Pavoni (1997)

Installations[link]

• Imagining Prometheus (2003)
• Luminaria (2003)

Discography (as composer)[link]

• Aquilarco - Polygram Records - #462546 (1998)
• Spasimo - Agora - #216 (2000)
• John Africa in "La formula del fiore" - Sensible Records: SSB 012, (1999)
• Viaggio in Italia - Agorà (AG 259) (2000)
• Violoncelles, vibrez! - Agorà: AG 155. (1998)
• Violoncelles, vibrez! (on Tracing Astor: Gidon Kremer Plays Astor Piazzolla) - Nonesuch: 79601 (2001)
• Canti rocciosi - I suoni delle Dolomiti (2001)
• Works - Sony Music: DED 519769 2 (2005)^[3]
• Heimat Terra, Fiddle Files (on The Magic of Wood: From Lutherie to Music) - Dynamic: 5092 (2005)
• We were trees - Sony/BGM 88697314382 (2008)
• Astrolabioanima - Odd Times Record: OTR 001 (2008)
• Sonnets et Rondeaux - Cobra Records: CBRA 35 (2012)

Notes[link]

External links[link]

Video[link]

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