Crossover design in pharmacy research

OBJECTIVE: Reports of pharmacy research using crossover designs were reviewed to determine if the studies adequately consider interaction effects and use appropriate statistical analyses. DATA SOURCES: All crossover studies published in DICP, The Annals of Pharmacotherapy during 1988 and 1989 were analyzed. STUDY SELECTION: Reports of crossover studies were included only if at least two treatments were applied in a different order to two or more groups of subjects. DATA EXTRACTION: The principal characteristics of crossover studies and the critical design variables were listed and each study analyzed according to these variables. The critical design variables included consideration of period, sequence, and carryover effects as well as the presentation of data by groups and the use of multivariate statistical analysis. The analysis was conducted independently by each author and conflicts were discussed until consensus was obtained. RESULTS: A total of 11 crossover studies were identified: 6 were bioavailability trials, 3 were treatment comparisons, and 2 had multiple objectives. The possibility of period, sequence, or carryover effects was less with bioavailability studies than with treatment comparisons. Only 1 study presented data by group and only 4 studies used multivariate analysis. The crossover design appears more appropriate for bioavailability trials than for treatment trials in pharmacy research. Analysis of data from crossover designs could be improved by presenting the data for each treatment group and using multivariate statistical analysis.