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Difficulty: EasyBias and Confounding in Research

A medical researcher evaluates the association between regular consumption of processed meats and the incidence of colon cancer using a large national database. The initial crude analysis demonstrates a statistically significant increased risk of colon cancer among individuals who consume high amounts of processed meats. Suspecting another variable might be influencing this result, the researcher stratifies the data by the participants' level of daily physical activity. After stratification, the risk of colon cancer is no longer elevated in either the low physical activity group or the high physical activity group. Which of the following terms best describes the role of physical activity in this study?

  1. ConfoundingAnswer
  2. B
    Effect modification
  3. C
    Selection bias
  4. D
    Measurement bias
  5. E
    Recall bias

Answer

Confounding
The scenario describes confounding. Confounding occurs when a third variable is associated with both the exposure (processed meat) and the outcome (colon cancer) but is not on the causal pathway. When the researcher stratified by physical activity, the apparent association between processed meat and colon cancer vanished in all groups. This indicates that physical activity was the true cause of the association seen in the crude analysis, making it a confounder.

Step-by-Step Solution

1
Analyze the initial crude association.
There is a statistically significant association between processed meat consumption and colon cancer.
This establishes the baseline finding before adjusting for other variables.
2
Analyze the effect of stratification on the data.
When stratified by physical activity, the association between processed meat and colon cancer disappears in all subgroups.
Observing how an association changes after stratification determines if a third variable is a confounder or an effect modifier.
3
Interpret the stratification results based on epidemiologic principles.
Because the stratum-specific risks are identical to each other and show no association, the initial crude finding was entirely due to the third variable.
A confounder is a third variable associated with both the exposure and the outcome. Stratification removes its effect, revealing the true association.

Key Concept

Identifying confounding through stratified analysis
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Topics

Bias and Confounding in Research

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