For each of the following statistical relationships, decide whether the directionality problem is present and think of at least one plausible third variable.

a. People who eat more lobster tend to live longer.

b. People who exercise more tend to weigh less.

c. College students who drink more alcohol tend to have poorer grades.

A. The problem is present - third variable could be that living in Maine can lead to eating more lobster and living longer.

B. The problem is present - perhaps weighing less means working out more.

C. The directionality problem is not present.

A. Directionality problem and third variable are present.

B. No directionality problem; third variable: eating habits.

C. Directionality problem; third variable: intelligence.

Explanation:

The directionality problem refers to the possibility that the first variable causes changes in the second one, and vice versa.

For example, people become aggressive watching violence on TV or is it that agressive people like to watch violent programs?

A People who live longer (due to a healthy environment for example) have more time to eat more lobster; the 3rd variable being living in Maine.

B There is no directionality problem; weighing less is no cause; the 3rd variable might be the diet; I know of people who work out a lot and eat even more.

C There is a directionality problem: when you have poor grades you might console yourself with alcohol. The 3rd variable is intelligence; if you're smart you can drink a lot and still get good grades.