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Tuesday, December 4, 2012

Incidence and Prevalence



The number of new cases emerging in a specific period and area
The number of new cases occurring in a defined population during specific period of time
Incidence= Number of new cases of specific diseases (during a given time period     × 1000
                     Population at risk during the same interval
Incidence demonstrates about:
·         New cases of the diseases during a specified period of time in a specified population and area
·         Incidence is not influenced by the duration of the disease
·         The of incidence is restricted to only acute diseases

Cumulative incidence:

CI = Number of disease people           × 100
        Total number of healthy people

Attack rate:

A.R. = number of disease people   × 100
            Number of exposed people


The number of existing cases occurring in a defined population during a specific period of time
The term disease prevalence refers to all the existing cases in a specified area and in a specified time.
Prevalence = Total number of individuals having attribute or disease at a particular time
                        The population at risk of having the attribute or disease in a particular time

Types of prevalence:

         i.            Point prevalence: specific to days, month, age or sex
       ii.            Period prevalence: specific to period of time such as from July 2010 to July 2011


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