Coffee Drinking and Sexual Habits. From a sample of 13,912 households in Washtenaw County, Michigan, 2,993 persons were identified as being 60 years old or older. Of these, 1,956 agreed to participate...

Coffee Drinking and Sexual Habits. From a sample of 13,912 households in Washtenaw County, Michigan, 2,993 persons were identified as being 60 years old or older. Of these, 1,956 agreed to participate in a study. The following table is based on data from the married women in this sample who answered the questions about whether they were sexually active and whether they drank coffee. (Data from A. C. Diokno et al., “Sexual Function in the Elderly,” Archives of Internal Medicine 150 (1990): 197–200.) (a) What type of sampling scheme was this? To what population can inferences be made? (b) Are these data more useful for investigating whether coffee drinking causes decreased sexual activity or whether sexual activity causes decreased coffee drinking? (c) If it is desired to treat sexual activity as a categorical response, does the inequality of the row totals create a problem?