To enhance the credibility of such retrospective comparisons , we propose the application of the following adjustments to significance levels obtained from standard statistical methodology : ( 1 ) a significance test for the lower bound of the 95 % confidence interval for the observed difference , ( 2 ) a conservative Bonferroni method of adjustment for multiple comparisons , ( 3 ) an adjusted p-value calculated using Scheffe 's single-step method , and ( 4 ) Bayesian 95 % credibility intervals with a prior centered at zero .