Each of the following conclusions is based on a relationship between X and Y that is completely spurious. For each one: i. Think up a plausible variable, Z, that defines a compositional difference across the values of X.
ii. Describe how Z creates the relationship between X and Y.

Example: Red cars (X) are more likely to be involved in accidents (Y) than are nonred cars.
Conclusion: If red cars are banned, the accident rate will decline. (i) Driver age (Z). (ii) Drivers of red cars are younger than drivers of nonred cars. Younger people have higher accident rates (Y) than do older people. As car color (X) varies, driver age (Z) varies, which causes accident rates (Y) to change.

a. Students who smoke (X) earn lower grades (Y) than students who do not smoke.
Conclusion:
b. Expectant mothers who drink bottled water (X) have healthier babies (Y) than do expectant mothers who do not drink bottled water.
Conclusion:
c. Tea drinkers (X) are more likely to be Democrats (Y) than are non–tea drinkers.
Conclusion: