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 f liers 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 f lu season. They asked whether the children had been immunized, whether the parents had received f lu shots, and who in the family had contracted the f lu.