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Statistical Measures

Morbidity Frequency Measures

Prevalence Rates

Point vs. Period Prevalence
The amount of disease present in a population obviously changes over time. Sometimes, we want to know how much of a particular disease is present in a population at a single point in time, a sort of snapshot view.

  • Point Prevalence: For example, we may want to find out the prevalence of TB in Community A today. To do that, we need to calculate the point prevalence on a given date.
    • The numerator would include all known TB patients who live in Community A that day. That information could be determined from a TB case registry.
    • The denominator would be the population of Community A that day.
    Example: A review of patients reported to the tuberculosis registry in Midville revealed that as of July 1, 2005 there were 35 cases that had not yet completed therapy. The most recent population estimate for Midville was 57,763. The prevalence of TB in Midville on July 1, 2005 was:
                 
    • Point prevalence is useful in comparing different points in time to help determine whether an outbreak is occurring. In this case, we could also calculate point prevalence of TB for July 1, 2004, July 1, 1995 or other relevant points of comparison.