Confounding Variables Statistics Example 3
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Example 3
mediumA study finds that people who own swimming pools are more likely to have skin cancer. Identify a possible confounding variable and explain how random assignment could address it.
Solution
- 1 Step 1: Confounding variable: sun exposure. People who own pools likely spend more time outdoors in the sun, which increases both pool ownership (outdoor lifestyle) and skin cancer risk (UV exposure).
- 2 Step 2: In theory, randomly assigning people to own or not own pools would distribute sun exposure habits equally between groups, isolating the pool ownership effect. However, this is impractical, making this a case where only observational data is available.
Answer
Sun exposure is a confounding variable — pool owners likely spend more time in the sun, which is the actual risk factor for skin cancer. Random assignment (impractical here) would balance sun exposure between groups.
Confounding variables create misleading associations. The association between pool ownership and skin cancer is driven by sun exposure, not by the pool itself. Recognising potential confounders helps us avoid drawing incorrect causal conclusions from observational data.
About Confounding Variables
A confounding variable is a third variable that influences both the independent variable and the dependent variable simultaneously, creating a spurious association between them that can be mistaken for a direct causal relationship. Confounders are a major threat to the internal validity of observational studies.
Learn more about Confounding Variables →More Confounding Variables Examples
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