77 Physical activity of obese young adults. The International Journal of Obesity (Jan. 2007) conducted a study of the physical activity of obese young adults. For two groups of young adults—13 obese and 15 of normal weight—

researchers recorded the total number of registered movements

(counts) of each young adult over a period of time.

Baseline physical activity was then computed as the number of counts per minute (cpm). Four years later, physical activity measurements were taken again—called physical activity at follow-up .

a. For the 13 obese young adults, the researchers reported a correlation of r = .50 between baseline and follow-up physical activity, with an associated p -value of .07. Give a practical interpretation of this correlation coefficient and p -value.

b. Refer to part a . Construct a scatterplot of the 13 data points that would yield a value of r = .50.

c. For the 15 young adults of normal weight, the researchers reported a correlation of r = -.12 between baseline and follow-up physical activity, with an associated p -value of .66. Give a practical interpretation of this correlation coefficient and p -value.

d. Refer to part c . Construct a scatterplot of the 15 data points that would yield a value of r = -12.