For the following observational studies, indicate whether they are prospective or retrospective.

a) An airline was concerned that new security measures might discourage air travellers. A year after the new security restrictions were put into place, the airline compared the miles travelled by its 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.