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Difficulty: HardMeasures of Association and Impact

Match each clinical study scenario to the most appropriate statistical measure of association or impact used to interpret its results.

  • A study identifies hospitalized patients with Guillain-Barré syndrome and compares their prior vaccination histories to those of matched patients without the syndrome.Odds Ratio (OR)
  • An observational study follows initially healthy adults with and without chronic NSAID use over 15 years to compare the incidence of new-onset chronic kidney disease.Relative Risk (RR)
  • A randomized clinical trial of a new biologic agent reports the inverse of the absolute difference in adverse event rates between the treatment and placebo groups.Number Needed to Harm (NNH)
  • A state health department calculates the percentage of total lung cancer cases in the population that would be eliminated if radon exposure were completely eradicated.Population Attributable Fraction (PAF)

Answer

The Guillain-Barré scenario is a case-control study matching Odds Ratio. The NSAID scenario is a cohort study matching Relative Risk. The inverse absolute difference matches Number Needed to Harm. The population preventable percentage matches Population Attributable Fraction.
Case-control studies use Odds Ratio because incidence cannot be determined. Cohort studies measure true incidence and therefore report Relative Risk. Number Needed to Harm is mathematically defined as the inverse of the Absolute Risk Increase. Population Attributable Fraction measures the preventable proportion of disease in the entire population.

Step-by-Step Solution

1
Analyze the first scenario regarding Guillain-Barré syndrome and vaccination.
The study identifies patients based on outcome (disease) and looks backward at exposure. This is a case-control design.
Identifying the study design is the first step because case-control studies cannot measure true incidence.
2
Select the appropriate measure for the case-control design.
Matches with Odds Ratio (OR).
Case-control studies use OR to estimate relative risk since absolute incidence rates are determined by the investigator's sampling, not natural disease occurrence.
3
Analyze the second scenario regarding NSAID use and chronic kidney disease.
The study groups patients by exposure and follows them prospectively. This is a cohort design.
Cohort studies follow patients over time to measure the actual incidence of disease.
4
Select the appropriate measure for the cohort design.
Matches with Relative Risk (RR).
Because incidence can be directly measured, RR is the standard and most intuitive measure of association.
5
Analyze the third scenario describing the inverse of the absolute difference in adverse events.
Matches with Number Needed to Harm (NNH).
By definition, NNH = 1 / Absolute Risk Increase (ARI).
6
Analyze the fourth scenario determining the proportion of total disease cases prevented in a population.
Matches with Population Attributable Fraction (PAF).
PAF (or Population Attributable Risk Percent) specifically calculates the percentage of total disease in an entire population that is attributable to an exposure.

Key Concept

Selecting the appropriate biostatistical measure (OR, RR, NNH, PAF) depends fundamentally on the study design (case-control vs. cohort/trial) and the specific epidemiological question being asked.
Estimated Time:2m 0s
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Topics

Measures of Association and Impact

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