Tfelt-Hansen P, Nielsen S L
Department of Neurology, Københavns Amtssygehus i Gentofte, Hellerup, Denmark.
Neuroepidemiology. 1987;6(4):214-9. doi: 10.1159/000110122.
Based on a multicenter double-blind crossover prophylactic migraine trial (n = 96), the relative effectiveness of the crossover design versus group comparison was evaluated. If a 'time effect' is taken into account in the statistical model, the crossover design was estimated to be 10-11 times more effective than the group comparison. With more traditional statistical methods using paired and unpaired t tests, the crossover design was estimated to be 4 times more powerful than the group comparison. Based on the t test, sample size tables for numbers of patients needed for detecting effect differences from 10 to 50% with powers from 0.6 to 0.9 in a crossover and a group comparison are presented. These calculations are based on only one trial, and it is recommended that similar estimations of sample variability should be done in other previous trials.
基于一项多中心双盲交叉预防性偏头痛试验（n = 96），对交叉设计与组间比较的相对有效性进行了评估。如果在统计模型中考虑“时间效应”，交叉设计的有效性估计比组间比较高10至11倍。使用配对和非配对t检验等更传统的统计方法，交叉设计的效能估计比组间比较高4倍。基于t检验，给出了在交叉设计和组间比较中，检测10%至50%效应差异且效能为0.6至0.9时所需患者数量的样本量表。这些计算仅基于一项试验，建议在其他先前的试验中进行类似的样本变异性估计。
