A report in a medical journal notes that the risk of developing Alzheimer’s disease among subjects who regularly opted to take the drug ibuprofen was about half the risk of those who did not. Is this good evidence that ibuprofen is effective in preventing Alzheimer’s disease?

a. Yes, because the study was a randomized, comparative experiment.

b. No, because the effect of ibuprofen is confounded with the placebo effect.

c. Yes, because the results were published in a reputable professional journal.

d. No, because this is an observational study. An experiment would be needed to confirm (or not confirm) the observed effect.

e. Yes, because a 50% reduction can’t happen just by chance.