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How Prevalence is Calculated

 
More info on Basic Information About Tables:
 How Prevalence is Calculated
   

To calculate prevalence first determine the following values:

  • The number of occurrences of a given condition or health indicator during a specified time period regardless of when the health indicator began. (This number includes both new cases and old cases. Old cases represent people who still had the condition or health indicator during some portion of the specified time interval.)
  • The size of the population in which the condition or health indicator occurs.

Prevalence is then calculated by dividing the number of occurrences of the health indicator during the specified time period by the size of the population in which the health indicator occurs. The result is expressed as a percentage.
The formula for calculating prevalence in PedNSS and PNSS is shown below.

Prevalence= persons with a given health indicator during a specified time period
population during the same time period
X 100

Using this formula, the prevalence of low birthweight in the following example is 9.3 percent.

Low Birthweight
Prevalence

= number of infants <2500 grams born during the reporting period
population during the same time period
X 100
Example:   5,807
62,441
 X 100  = 9.3 percent

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United States Department of Health and Human Services
Centers for Disease Control and Prevention
National Center for Chronic Disease Prevention and Health Promotion
Division of Nutrition and Physical Activity

This page last updated March 04, 2010

United States Department of Health and Human Services
Centers for Disease Control and Prevention
National Center for Chronic Disease Prevention and Health Promotion
Division of Nutrition and Physical Activity