Testing Crossover Studies for Carryover Effects

Abstract

For the study of cardiovascular disease, for instance, hypertension and angina pectoris, properly de signed crossover studies are to be preferred over parallel-design stud ies. Many statisticians now propose that these studies should always be tested for carryover effects. In the present paper the author analyzes the crossover studies published after No vember, 1985, in two general and two specialist journals (New England Journal of Medicine, Lancet, Angiol ogy, British Heart Journal). Of 73 pa pers only 23 (32%) consider the possi bility of carryover effects. Of these latter papers 12 (16%) perform sta tistical tests for these effects. The results of these tests were shown in only 7 papers (10%). It is concluded that there is a discrepancy between the statistical recommendations and the data presented in the literature.