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In 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%. [5] Prevalence is a term that means being widespread and it is distinct from incidence.
The prevalence of mental illness is higher in more unequal rich countries. The prevalence of mental disorders has been studied around the world, providing estimates on how common mental disorders are. Different criteria or thresholds of severity have sometimes been used.
Prevalence can also be measured with respect to a specific subgroup of a population. Incidence is usually more useful than prevalence in understanding the disease etiology: for example, if the incidence rate of a disease in a population increases, then there is a risk factor that promotes the incidence.
The positive predictive value (PPV), or precision, is defined as = + = where a "true positive" is the event that the test makes a positive prediction, and the subject has a positive result under the gold standard, and a "false positive" is the event that the test makes a positive prediction, and the subject has a negative result under the gold standard.
For example, suppose we are interested in estimating the prevalence of a disease in a population. The base rate would be the proportion of individuals in the population who have the disease. If we observe a positive test result for a particular individual, we can use Bayesian analysis to update our belief about the probability that the ...
Epidemiology, literally meaning "the study of what is upon the people", is derived from Greek epi 'upon, among' demos 'people, district' and logos 'study, word, discourse', suggesting that it applies only to human populations.
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However, this does not compensate for (former mentioned) effect of any difference between pre-test probability of an individual and the prevalence in the reference group. A method to compensate for both sources of inaccuracy above is to establish the relative risks by multivariate regression analysis. However, to retain its validity, relative ...