Measures of Occurrence

2a Measures of Occurrence. Measures of occurrence are usually reported in descriptive epidemiological studies. The incidence of disease is the number of new cases occurring during a defined time period, whereas prevalence is the number of individuals with disease at a specified time period. The formula for incidence and prevalence rates are as follows  

Number of new cases of a disease in a specified time period Population at risk during that time period 

Number of existing cases of disease at a single time point Total population at that point in time 

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After a study has been conducted, the data are analyzed to see whether an association is observed. This section briefly defines the two major measures of occurrence (incidence and prevalence) and discusses measures of associations in detail, focusing on the most common measures used in the epidemiological study designs described above, such as correlation coefficient, relative risk, and odds ratio. 

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