Read A Data Table Basic Information Demographic Tables Prevalence Tables Trend Tables Review Data Quality Interpret Data Disseminate Data

# How To... - Read A Data Table - 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