Abstract
"The Statistical Principles for Clinical Trials" agreed in The International Conference on Har-monization (ICH) adopts a new principle for dealing with the treatment-by-centre interaction. It recommended that the efficacy of a new treatment might be confirmed by a hypothesis test based on an ANOVA model without treatment-by-centre interaction. This recommendation is not consistent with the conventional method, which preliminarily uses the test for interaction before testing the existence of the main effect on an ANOVA model.
This paper investigated the plausibility of this recommendation compared with the conventional method through the evaluation of the probability of approving the efficacy of the new treatment.
It quantitatively clarified that the recommended procedure highly suppressed the probability when the interaction existed, i.e., the difference of the probability between the two method was as large as 17% when 10 patients in each of two groups were recruited for each of five centres and the in-teraction effect was observable in spite of the existence of a fairy big main effect. The observed tendency was retained even if the number of patients allocated to each of two groups compared was not identical.
This indicates that the ICH recommendation is consistent with the strategy of ICH that the new treatment should not be approved without further examination on the physical implications of the interaction when it exists.
