EXAMPLE 14.26 Software Output for Confidence Intervals

CASE 14.2 For simultaneous 95% Bonferroni confidence intervals, SPSS gives the output in Figure 14.17 for the data in Case 14.2. We are 95% confident that all three intervals simultaneously contain the true values of the population mean differences. After rounding the output, the confidence interval for the difference between the mean of the Basal group and the mean of the DRTA group is (−10.36, −1.00). This interval does not include zero, so we conclude that the DRTA method results in higher mean comprehension scores than the Basal method. This is the same conclusion we obtained from the significance test, but the confidence interval provides us with additional information about the size of the difference.