Table 9.10 shows data on the age (in months) at which 21 children said their first word and their score on a later test of mental aptitude [21]. Use a regression equation to see if there is a statistical relationship.

a. Which variable did you use as the dependent variable? Explain your reasoning.

b. What is the two-sided P value for the slope?

c. Plot the residuals for your regression equation with X on the horizontal axis and draw a horizontal line at zero on the vertical axis. What pattern or other peculiarity do you see in the residuals?

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Age Test Age Test Age Test Age Test Age Test Age Test Age Test 15 95 9 91 18 93 20 94 10 83 10 100 17 121 26 71 15 102 11 100 7 113 11 84 12 105 11 86 10 83 20 87 8 104 9 96 11 102 42 57 10 100