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Difficulty: EasyMeasures of Disease Frequency and Association

A 4545-year-old man presents to the clinic to discuss his risk of developing pancreatic cancer. His father was recently diagnosed with the disease, and the patient is concerned about his own long-term occupational exposure to industrial dyes as a textile worker. The physician reviews the medical literature and finds a recent study that selected 200200 individuals with pancreatic cancer and 400400 individuals without the disease. The researchers subsequently analyzed the participants' past occupational records to determine their previous exposure to industrial dyes. Which of the following metrics was most likely reported in the study to quantify the association between dye exposure and pancreatic cancer?

  1. Odds ratioAnswer
  2. B
    Relative risk
  3. C
    Attributable risk
  4. D
    Absolute risk reduction
  5. E
    Positive predictive value

Answer

Odds ratio
The clinical vignette describes a study where investigators first selected individuals based on their disease status (individuals with and without pancreatic cancer) and then looked back at their history to assess an exposure (industrial dyes). This is the classic design of a case-control study. In case-control studies, the researchers artificially determine the proportion of diseased individuals in the study, meaning they cannot calculate the true incidence (new cases over time in a population at risk). Because incidence is required to calculate relative risk and attributable risk, these metrics cannot be used. Instead, case-control studies use the odds ratio to quantify the association between an exposure and a disease.

Step-by-Step Solution

1
Identify the study design by determining how the researchers selected their participant groups.
Participants were selected based on the presence or absence of the outcome (pancreatic cancer), making this a case-control study.
The method of participant selection determines the study design, which in turn dictates the valid statistical measures.
2
Determine the appropriate measure of association for a case-control study.
Because disease incidence cannot be calculated when the investigator fixes the number of cases and controls, relative risk cannot be used. The appropriate measure is the odds ratio.
The odds ratio provides an estimate of relative risk when incidence data is unavailable, by comparing the odds of exposure among cases to the odds of exposure among controls.

Key Concept

Selection of statistical measures based on epidemiological study design
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Topics

Measures of Disease Frequency and Association

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