If a test of the difference is significant, then the direction of the difference is established because the values in the confidence interval are either all positive or all negative. Looking at non-si...If a test of the difference is significant, then the direction of the difference is established because the values in the confidence interval are either all positive or all negative. Looking at non-significant effects in terms of confidence intervals makes clear why the null hypothesis should not be accepted when it is not rejected: Every value in the confidence interval is a plausible value of the parameter.