Prevalence is the proportion of cases or disease states that exist in a population at any given time. Prevalence is established using cross-sectional research designs. Measures of prevalence can be used to generate odds ratios for outcomes occurring given an exposure or non-exposure. It is calculated when data is collected in a retrospective fashion.
Incidence is the number of new cases or disease states that occur in a population. Incidence is established in cohort designs. Measures of incidence are used to establish the relative risk of an outcome given treatment or no treatment. It is calculated when data is collected in a prospective fashion.
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