To determine if carrot juice helps improve heart conditions, a juicing company asks a random sample of 100 adults about whether or not they drink carrot juice and their heart condition. The company finds an association between drinking carrot juice and healthy heart conditions. Which statement is true about a possible confounding variable?
Answer
A
A possible confounding variable is the amount of exercise. Those that drink carrot juice may be more concerned about their health and exercise more, which explains the healthy heart conditions.
B
A possible confounding variable is eating dinner at a fast-food restaurant. Those that eat at fast-food restaurants are more likely to not drink carrot juice and the fast food would explain the healthy heart conditions.
C
A possible confounding variable is the amount of exercise. Those that drink carrot juice are not concerned about their health and are more likely to not exercise, which does not improve heart conditions.
D
A possible confounding variable is eating fast food. Those that drink carrot juice are more concerned about their health and are more likely to not eat fast food which does not improve heart conditions.
Explanation
A confounding variable is another factor related to both the explanatory variable and the outcome that could help explain their association. People who choose to drink carrot juice may also be more health-conscious and exercise more, and exercise can contribute to healthier hearts. So the association may be partly explained by exercise rather than carrot juice alone; this matches choice A.
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