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Difficulty: MediumMeasures of Association and Impact

Match each clinical research scenario with the most appropriate epidemiological measure of association or impact that should be calculated.

  • Investigators recruit 100 patients with a newly diagnosed rare hepatic angiosarcoma and 200 healthy volunteers, then compare their past occupational exposures to vinyl chloride.Odds ratio
  • A research team enrolls 10,000 disease-free adults and tracks them over two decades to compare the development of incident heart failure between those with and without baseline metabolic syndrome.Relative risk
  • A governmental health agency analyzes epidemiological data to estimate the proportion of all new asthma diagnoses in their metropolitan area that are directly due to industrial air pollution.Population attributable fraction
  • A multicenter randomized trial evaluates a new targeted biologic for severe psoriasis, specifically calculating how many individuals must receive the therapy rather than placebo to achieve skin clearance in one additional patient.Number needed to treat

Answer

Case-control studies utilize the odds ratio. Prospective cohort studies utilize relative risk. Estimating population-level disease burden utilizes the population attributable fraction. Evaluating the clinical threshold to achieve one positive outcome utilizes the number needed to treat.
Matching epidemiological measures to their corresponding study designs or clinical applications requires understanding the directionality of the research and the mathematical definitions of the metrics. Case-control studies use odds ratios because incidence cannot be calculated. Cohort studies typically use relative risk because they measure true incidence. Public health burden assessments use the population attributable fraction to account for exposure prevalence. Clinical trial absolute benefit is expressed as the number needed to treat to help physicians communicate realistic expectations to patients.

Step-by-Step Solution

1
Identify the study design or primary goal in the first scenario.
The study starts with a disease (angiosarcoma) and looks backward at past exposure.
This characterizes a retrospective case-control study.
2
Determine the correct metric for a case-control study.
Odds ratio.
True disease incidence cannot be calculated directly in case-control studies because the researcher dictates the number of cases and controls, precluding the use of relative risk.
3
Identify the study design in the second scenario.
The study starts with an exposure (metabolic syndrome) and tracks the future development of disease.
This characterizes a prospective cohort study.
4
Determine the correct metric for a cohort study.
Relative risk.
Because patients are followed prospectively, true incidence rates can be calculated and compared directly via a ratio.
5
Analyze the goal of the third scenario.
The goal is to estimate the total disease burden in an entire population due to a specific factor.
This requires calculating the population attributable fraction, which accounts for both the risk of the exposure and its prevalence in the community.
6
Analyze the goal of the fourth scenario.
The goal is to calculate the absolute number of patients required to achieve one positive clinical outcome.
This is the precise definition of the number needed to treat (NNT).

Key Concept

Selection of appropriate epidemiological measures based on study design and clinical objective
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Topics

Measures of Association and Impact

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