1. Galileo's Data. Why is horizontal distance, rather than height, the response variable?

2. Brain Weight. Display 10.16 shows two possible influence diagrams relating the variables in the brain weight study of Section 9.1.2. If brain weight is directly associated with gestation period and litter size, as in part (a) of the figure, then animals that have approximately the same body size but different gestation period and different litter size should have different brain sizes, and scatterplots of brain size versus gestation and litter size individually should show some association. But the scatterplots can also show indirect associations, as in part (b) of the figure. If brain weight, gestation period, and litter size are all driven by body size, they should show mutual associations, whether or not a direct association exists. Can a statistical analysis distinguish between direct and indirect association? Explain how or, if not, why not.