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Difficulty: MediumMeasures of Association and Impact

A public health task force is reviewing several epidemiological studies and clinical trials to update national guidelines. For each described study objective below, select the most appropriate statistical metric used to report the findings.

  • Determining the number of patients who must receive a novel antiarrhythmic drug to prevent one additional stroke over a 3-year period.Number Needed to Treat (NNT)
  • Quantifying the absolute excess incidence of pulmonary toxicity directly linked to a chemotherapeutic agent among patients receiving the drug, compared to unexposed patients.Attributable Risk (AR)
  • Estimating the strength of association between asbestos exposure and mesothelioma using a retrospective design that selects participants based on their current disease status.Odds Ratio (OR)
  • Evaluating the proportion of total lung cancer incidence in a specific geographical region that could theoretically be eliminated if cigarette smoking were entirely eradicated.Population Attributable Risk Percent (PAR%)
  • Calculating the proportional decrease in the risk of myocardial infarction provided by a new statin relative to the baseline risk observed in the placebo group.Relative Risk Reduction (RRR)

Answer

The correct matches are: Preventing one event matches Number Needed to Treat (NNT); absolute excess incidence matches Attributable Risk (AR); case-control association matches Odds Ratio (OR); total population impact matches Population Attributable Risk Percent (PAR%); and proportional risk decrease matches Relative Risk Reduction (RRR).
Each clinical scenario describes the specific definition and application of a distinct biostatistical measure. Matching them correctly requires understanding the difference between relative measures (OR, RRR), absolute measures (AR, NNT), and population-level impact metrics (PAR%).

Step-by-Step Solution

1
Evaluate the first objective: determining the number of patients treated to prevent one event.
This defines the Number Needed to Treat (NNT).
NNT translates the absolute risk reduction into a tangible clinical metric of effort required to achieve one positive outcome.
2
Evaluate the second objective: quantifying absolute excess incidence in exposed versus unexposed groups.
This defines Attributable Risk (AR).
AR directly subtracts the incidence in the unexposed from the incidence in the exposed to find the excess risk.
3
Evaluate the third objective: estimating association in a retrospective study based on disease status.
This requires the Odds Ratio (OR).
Studies selecting based on disease status (case-control) cannot measure true incidence, making the Odds Ratio the mathematically valid measure of association.
4
Evaluate the fourth objective: finding the proportion of total population disease linked to an exposure.
This defines Population Attributable Risk Percent (PAR%).
PAR% looks at the burden of disease in the entire population (both exposed and unexposed) that can be attributed to the risk factor.
5
Evaluate the fifth objective: calculating the proportional decrease in risk relative to baseline.
This defines Relative Risk Reduction (RRR).
RRR compares the absolute difference in risk to the baseline risk in the control group, expressing the reduction as a percentage.

Key Concept

Selection and interpretation of appropriate epidemiological and statistical measures of association and impact based on study design and clinical objectives.
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Topics

Measures of Association and Impact

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