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Difficulty: MediumMeasures of Disease Frequency and Association

Match each clinical study scenario or derived statistic to the epidemiological measure of disease frequency or association it best represents.

  • A cross-sectional survey reveals that 12% of the residents in a nursing home have a pressure ulcer on the day of the assessment.Point Prevalence
  • A 5-year prospective study of 2,000 initially healthy adults reports that 40 participants developed newly diagnosed asthma during the follow-up period.Cumulative Incidence
  • An analysis of a randomized clinical trial indicates that the probability of myocardial infarction in patients taking a new drug is 0.6 times the probability in those taking a placebo.Relative Risk
  • A retrospective study of patients with gastric cancer and healthy controls finds that the exposure odds of prior Helicobacter pylori infection was 3 times higher in the cancer group.Odds Ratio
  • A randomized trial demonstrates an absolute risk reduction of 0.05 for stroke with a new anticoagulant, yielding a calculated metric of 20 to prevent one stroke.Number Needed to Treat (NNT)

Answer

12% nursing home assessment matches Point Prevalence; 5-year new asthma cases matches Cumulative Incidence; 0.6 probability ratio matches Relative Risk; H. pylori exposure odds matches Odds Ratio; Metric of 20 derived from 0.05 risk reduction matches Number Needed to Treat.
Each clinical scenario corresponds exactly to the epidemiological definition of its matched measure: existing cases (prevalence), new cases over time (incidence), ratio of probabilities (relative risk), ratio of exposure odds (odds ratio), and reciprocal of absolute risk reduction (number needed to treat).

Step-by-Step Solution

1
Analyze the first scenario regarding the nursing home assessment.
It describes existing disease at a single moment, indicating Point Prevalence.
Prevalence captures existing cases, not new cases.
2
Evaluate the second scenario involving the 5-year study of initially healthy adults.
It tracks the development of new asthma cases over time, indicating Cumulative Incidence.
Incidence requires an initially disease-free population monitored over a specified duration.
3
Assess the third scenario comparing probabilities in a clinical trial.
It describes the ratio of probabilities between two groups, indicating Relative Risk.
Relative Risk is calculated as the incidence in the exposed divided by the incidence in the unexposed.
4
Review the fourth scenario involving a retrospective comparison of gastric cancer patients and controls.
It calculates the ratio of exposure odds, indicating an Odds Ratio.
Case-control studies cannot directly measure incidence; they rely on odds ratios to estimate association.
5
Analyze the fifth scenario regarding absolute risk reduction of 0.05 yielding a value of 20.
It describes the calculation 1/ARR1 / ARR, indicating Number Needed to Treat.
Number Needed to Treat represents the number of patients required to receive the intervention to prevent one adverse outcome.

Key Concept

Epidemiological measures of disease frequency (incidence, prevalence) and association (relative risk, odds ratio, number needed to treat) each correspond to specific study designs and mathematical definitions.
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Topics

Measures of Disease Frequency and Association

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