Question: A person’s blood-clotting ability is typically expressed in terms of a “prothrombin time,” which is defined to be the interval between the initiation of the prothrombin-thrombin reaction and the formation of the final clot. Factors affecting the length of a person’s prothrombin time have profound medical significance. A recent study was undertaken to determine what effect, if any, aspirin has on this particular function. Twelve adult males participated in the study and their prothrombin times were measured before and three hours after each was given two aspirin tablets. The results are summarized in the following table. Does aspirin have any demonstrable effect on prothrombin time? Let α = 0.05.