Transient ischemic attacks and aspirin, stroke and death; negative studies and Type II error.

OF ALL SCIENTIFIC RESEARCH, clinical studies with their large number of recognized and unrecognized variables demand the most sophisticated and rigorous hypothesis testing and experimental design. Because of the small numbers and special charcteristics of a single center, large prospective double-blind cooperative studies have become necessary. Unfortunately, when multiple centers and investigators with different patient populations are involved, the probability of defects in design increases. Not unexpectly, the cooperative studies concerning the effect of the antiplatelet aggregating agent acetylsalicylic acid (aspirin) on stroke and death in patients with transient ischemic attacks (TIA) are no exception. Nevertheless, despite different weaknesses, past multiple center studies have always shown significant differences in favor of aspirin over placebo. In this issue, two additional prospective double-blind controlled cooperative studies are reported. For the first time one of these, the Danish study, did not conclude that aspirin was effective in reducing stroke and death. Although the French study was primarily a study of stroke and not TIAs, it did demonstrate a significant decrease in recurrent stroke and myocardial infarction in those who were treated with either aspirin or the combination of aspirin and dipyridamole. Thus, the results are similar to those of the Canadian and the United States cooperative studies.