To enhance the credibility of such retrospective comparisons , we propose the application of the following adjustments to significance levels obtained from standard statistical methodology : ( @ ) a significance test for the lower bound of the @ % confidence interval for the observed difference , ( @ ) a conservative Bonferroni method of adjustment for multiple comparisons , ( @ ) an adjusted p-value calculated using Scheffe 's single-step method , and ( @ ) Bayesian @ % credibility intervals with a prior centered at zero .