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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 |
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