Practice Confounding Variables in Statistics
Use these practice problems to test your method after reviewing the concept explanation and worked examples.
Quick Recap
A variable that influences both the independent and dependent variables, creating a spurious association that can be mistaken for causation.
Ice cream sales and drowning deaths correlate. Confounding variable: hot weather. It causes both! Without recognizing confounders, you'd wrongly blame ice cream for drowning.
Example 1
easyA study finds that children who have more books at home get higher test scores. A researcher concludes that buying more books will raise test scores. Identify the confounding variable.
Example 2
mediumHospitals A and B both perform a surgery. Hospital A has a 90% survival rate, Hospital B has 95%. However, Hospital A takes more high-risk patients. When only high-risk patients are compared, Hospital A has a higher survival rate. Explain this paradox.
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.
Example 4
hardA company claims its energy drink improves athletic performance because athletes who drink it run faster. However, the athletes were not randomly assigned — those who drank the energy drink also trained harder. (a) Identify the confounding variable. (b) Explain what 'controlling for' a confounding variable means. (c) How could the study be redesigned?