GPA and hours spent watching TV A study conducted among sophomores at Fairfield University showed a correlation of -0.69 between the number of hours spent watching TV and GPA. It was found that for each additional hour a week you spent watching TV, you could expect on average to see a drop of .0452, on a 4.0 scale, in your GPA.

a. Is there a causal relationship, whereby watching more TV decreases your GPA?

b. Explain how a student’s intelligence, measured by her/

his IQ score, could be a lurking variable that might be responsible for this association, having a common correlation with both GPA and TV-watching hours.

c. Sketch a hypothetical scatterplot (as we did in Figure 3.22 for the example on crime and education), labeling points by three IQ ranges, such that overall there is a negative trend, but the slope would be about 0 when we consider only students in a given IQ range. How would a student’s intelligence play a role in the association between GPA and TV-watching hours?