A report in a medical journal notes that the risk of developing Alzheimer’s disease among subjects who (voluntarily) regularly took the anti-inflammatory drug ibuprofen (the active ingredient in Advil) 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.

According to a study published in a medical publication, participants who (voluntarily) used the anti-inflammatory medicine ibuprofen (the active ingredient in Advil) on a regular basis had nearly half the risk of acquiring Alzheimer's disease as those who did not.

Individuals are purposely subjected to a treatment in order to measure their responses in an experiment.

Because this is an observational study, option (d) is the proper answer for this exercise: no, this is not good proof that ibuprofen is useful in preventing Alzheimer's disease. To corroborate the reported effect, an experiment would be required. While experiments can prove cause and effect when done correctly, observational studies virtually never can since there are simply too many complicating variables. Only a correlation between the explanatory and response variables may be shown in observational research.