Which inference method?

(a) How do young adults look back on adolescent romance?

Investigators interviewed 40 couples in their midtwenties. The female and male partners were interviewed separately. Each was asked about his or her current relationship and also about a romantic relationship that lasted at least two months when they were aged 15 or 16. One response variable was a measure on a numerical scale of how much the attractiveness of the adolescent partner mattered. You want to find out how much men and women differ on this measure.

(b) Are more than 75% of Toyota owners generally satisfied with their vehicles? Let’s design a study to find out. We’ll select a random sample of 400 Toyota owners. Then we’ll ask each individual in the sample: “Would you say that you are generally satisfied with your Toyota vehicle?”

(c) Are male college students more likely to binge drink than female college students? The Harvard School of Public Health surveys random samples of male and female undergraduates at four-year colleges and universities about whether they have engaged in binge drinking.

(d) A bank wants to know which of two incentive plans will most increase the use of its credit cards and by how much. It offers each incentive to a group of current credit card customers, determined at random, and compares the amount charged during the following six months.