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Difficulty: MediumMeasures of Association and Impact

A systematic review is aggregating data from various study designs to evaluate a new class of pharmacological agents. Different trials report their primary and secondary outcomes using distinct statistical metrics. Match each specific trial finding or calculation methodology to the most appropriate measure of association or impact.

  • The study notes a 15%15\% incidence of adverse gastrointestinal events in the treatment arm compared to 5%5\% in the placebo arm, reporting a raw difference of 10%10\%.Absolute Risk Increase (ARI)
  • Researchers determine that taking the reciprocal of the risk difference between treatment and control groups yields a value of 2525, indicating the patient volume required to receive the intervention to prevent one myocardial infarction.Number Needed to Treat (NNT)
  • A retrospective case-control study reports a cross-product ratio of 3.23.2 when comparing prior drug exposure in patients with acute hepatotoxicity versus those without the condition.Odds Ratio (OR)
  • A 10-year prospective cohort study indicates that the cumulative incidence of heart failure in the exposed group divided by the cumulative incidence in the unexposed group equals 1.41.4.Relative Risk (RR)

Answer

The correct matches link the raw difference in adverse event incidence to Absolute Risk Increase, the inverse of risk difference to Number Needed to Treat, the cross-product ratio in a case-control study to Odds Ratio, and the incidence rate ratio in a cohort study to Relative Risk.
Each specific clinical scenario strictly dictates a distinct epidemiological measure based on study architecture: subtraction of risks yields absolute differences (ARI/ARR), reciprocals of absolute differences yield NNT/NNH, prospective ratios yield Relative Risk, and retrospective cross-products yield Odds Ratios.

Step-by-Step Solution

1
Identify the metric describing the direct subtraction of adverse event rates.
Matches with Absolute Risk Increase (ARI).
ARI is calculated as the incidence of a harmful outcome in the exposed minus the incidence in the unexposed.
2
Identify the metric representing the reciprocal of the risk difference.
Matches with Number Needed to Treat (NNT).
NNT=1/ARRNNT = 1 / ARR, which quantifies the clinical impact of a beneficial intervention by showing how many patients must be treated to prevent one adverse event.
3
Identify the metric derived from cross-product ratios in a retrospective design.
Matches with Odds Ratio (OR).
Case-control studies cannot directly measure incidence, so they rely on the ratio of odds of exposure, calculated as (a×d)/(b×c)(a \times d) / (b \times c).
4
Identify the metric representing the ratio of incidence rates in a prospective design.
Matches with Relative Risk (RR).
Cohort studies follow patients forward in time, allowing direct calculation of incidence. The ratio of the exposed incidence to the unexposed incidence is the RR.

Key Concept

Selecting the appropriate biostatistical measure of association or impact requires understanding the underlying study design and the specific mathematical derivation of the metric.
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Topics

Measures of Association and Impact

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