An article entitled "Breast Milk Benefit" states: "In a review of 212 premature births from 1992 and 1993, the researchers found that 29% of the infants fed human milk acquired infections versus 47% of the babies fed formula."35
a. Was this an observational study or an experiment?
b. Which of these would be most worrisome here: confounding variables, people's behaviors affected by their awareness of participating in a prospective study, or people's faulty memories in a retrospective study?