Section 2.1 Solutions

2.3

1. If a child’s IQ score is above average, then we’d expect the child’s reading score to be above average. Likewise, if a child’s IQ score is below average, then we’d expect the child’s reading score to be below average. This indicates a positive association.

2. The four outlying observations are for children who have lower reading scores than we’d expect for their level of IQ score.

3. Ignoring outliers, the relationship is roughly linear, but only moderately strong (there’s a lot of variation in the plot).

2.9

The scatterplot is shown below. The relationship between brain activity and social distress is positive, linear, and strong, and there are no outliers present. From this study, it appears that brain activity in the pain region really is directly related to the distress from social exclusion.

2.13

a. The plot is shown below.

b. Overall, the relationship between metabolic rate and lean body mass is positive, linear and strong. The relationship within women is stronger than the relationship within men (there is more variation in the male observations). Also, the values of both variables are generally higher for men than for women.

2.18

1. The plot is shown below. (The mean growths are 10.65, 10.425, 5.6, and 5.45. respectively.)

2. There is little difference in average growth between 0 nematodes and 1000 nematodes; also there is little difference in average growth between 5000 nematodes and 10000 nematodes. But there is a large drop in average growth between 1000 and 5000 nematodes.