Deaths from highway accidents went down after the adoption of a national 55 mile-per-hour speed limit. Can we be confident that the lower speed limit caused the drop in deaths?
A) Yes, because the study was a randomized, comparative experiment.
B) No, because the effect of lower speed limits is confounded with the effect of better highways and safer cars.
C) Yes, because a drop in deaths over several years can't happen just by chance.
D) No, because of the placebo effect.
E) Yes, because correlation implies causation.

Question

Quizplus · Accepted Answer

The effect of lower speed limits cannot be isolated from other factors like better highways and safer cars that could have also contributed to the drop in deaths. A randomized, comparative experiment would be necessary to establish causation. The fact that the drop in deaths persisted over several years does not necessarily imply causation. The placebo effect is not relevant in this context. Finally, correlation does not imply causation.

Deaths from Highway Accidents Went Down After the Adoption of a National