Updated: 12/28/2021

Other Measures Of Disease Occurrence

Review Topic
  • Snapshot
    • There is a city with a population of 500,000. There are 20,000 women of childbearing age. In the year 2020, there are 20 maternal deaths and 200 live births. The maternal mortality rate is 20/200 = 0.1.
  • Introduction
    • Overview
      • in addition to prevalence and incidence, there are other methods of measuring the occurrence of disease
    • Crude mortality rate
      • describes the total number of deaths per years per 1,000 people
      • equation
        • number of deaths/total population size
    • Cause-specific mortality rate
      • describes the mortality rate caused by a certain disease/cause
        • e.g., aggressive malignancy
      • equation
        • number of deaths by a certain disease/total population size
    • Case-fatality rate
      • equation
        • number of deaths by a certain disease/total population affected by the disease
    • Attack rate
      • a type of incidence measure that is usually used in the epidemiology of infectious disease
        • e.g., gastrointestinal infection in patients caused by contaminated food
      • equation
        • number of patients with the disease/total population at risk
    • Maternal mortality rate
      • equation
        • number of maternal deaths/number of live births
    • Crude birth rate
      • equation
        • number of live births/total populations size
    • Prospective and Retrospective Studies
      • Prospective studies
        • patients enrolled before data collection
        • participants followed over time
        • data collected on exposures and outcomes as they arise
      • Retrospective studies
        • involve collecting historical information from a sample of patients
        • enrollment occurs after exposure and outcome have already occurred
      Case-Control Study
      • Retrospective (almost always)
      • Compares patients with and without disease to asses their odds of a certain exposure
      • Odds ratio (OR) is measure of disease association
        • OR= odds of exposure among cases/odds of exposure in non-cases = ad/bc
          • odds of exposure among cases=# cases with exposure/# cases without exposure = a/c
          • odds of exposure among non-cases=# non-cases with exposure/# non-cases without exposure=b/d
      • "How much more likely is it that patients with cirrhosis have been exposed to heavy alcohol use compared to controls?"
      Cohort Study
      • Can be eitherprospectiveorretrospective
      • Compares groups with and without an exposure to assess associations with subsequent disease
      • Relative risk (RR) is measure of disease association
        • RR= incidence rate in exposed group/incidence rate in unexposed group = [a/(a+b)]/[c/(c+d)]
          • incidence rate in exposed group=# of exposed cases/(# total exposed cases and non-cases) = a/(a+b)
          • incidence rate in unexposed group=# of unexposed cases/(# total unexposed cases and non-cases)=c/(c+d)
      • "How much more likely are patients to develop cirrhosis if they are exposed to heavy alcohol use?"
      Cross-Sectional Study
      • Exposure and outcome are assessed simultaneously
      • Ascertains association not causality
      • Prevalenceis measure of disease association
      • "How much higher is the proportion of cirrhosis patients with heavy alcohol use compared to those without cirrhosis?"

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