Problem: Refer to Thought Question at the beginning of this chapter. The headline was based on a study in which a representative sample of over 400,000 adults in the United States were asked a series of questions, including level of education and on how many of the past 30 days they felt physically and emotionally healthy.

a. What were the intended explanatory variable and response variable for this study?

b. Explain how each of the "difficulties and disasters in observational studies" (Section 5.5) applies to this study, if at all.

Question: A study to see whether birds remember color was done by putting birdseed on a piece of red cloth and letting the birds eat the seed. Later, empty pieces of cloth of varying colors (red, purple, white, and blue) were displayed. The birds headed for the red cloth. The researcher concluded that the birds remembered the color.

a. Using the terminology in this chapter, give an alternative explanation for the birds' behavior.

b. Suppose 20 birds were available and they could each be tested separately. Suggest a better method for the study than the one used.