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 among 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

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

Explanation:

The study that has been reported in the question does not provide any association or correlation results and presents a result that has been observed. Hence, this is an observational study. Although, cause and effect research studies might be able to provide some evidence in this regard however, on the basis of the presented evidence, it cannot be suggested that ibuprofen is effective in preventing Alzheimer's disease. Therefore, option d which states that this is an observational study and that an experiment would be needed to confirm (or not confirm) the observed effect is correct.