1. For the following observational studies, indicate whether they are prospective or retrospective.
a) A company looked at a sample of returned registration cards to estimate the income level of households that pur- chased their product.
b) A retail outlet encouraged customers to join their "fre- quent buyers" program and studied whether those who joined were more likely to make use of discount coupons than those who were not members.
2. For the following observational studies, indicate whether they are prospective or retrospective studies.
a) An airline was concerned that new security measures might discourage air travelers. A year after the new security restrictions were put into place, the airlines compared the miles traveled by their frequent fliers before and after the change.
b) Does giving children a flu shot protect parents? Researchers questioned a random sample of families at the end of a flu season. They asked whether the children had been immunized, whether the parents had received flu shots, and who in the family had contracted the flu.