Consequently several procedures have been developed

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: set of all pairwise comparisons among population means. In our previous Drug example, the possible pairwise comparisons are: Drug 1 with Drug 2, Drug 1 with Drug 3, and Drug 2 with Drug 3. To compare the pair of means we could … Compute a confidence interval for the difference between the two population means and see if 0 falls in the interval or not. Perform a test of hypotheses to assess if the two population means differ significantly. When many statistical tests are done there is an increased risk of making at least one type I error (erroneously rejecting a null hypothesis). Consequently, several procedures have been developed to control the overall family type I error rate or the overall family confidence level when inferences for a set (family) of multiple comparisons are done. Tukey’s procedure is one such procedure for the family of pairwise comparisons. If the family error rate is not a concern, Fisher’s procedure is used. Try It! Comparing 3 Drugs In the comparison of the three drugs, we rejected the null hypothesis at the 5% significance level. We follow with a multiple comparison procedure to determine which group means are significantly different from each other. SPSS multiple comparisons using Tukey's method and a family confidence level of 95%: Multiple Comparisons Dependent Variable: TIME Tukey HSD (I) DRUG 1 2 3 (J) DRUG 2 3 1 3 1 2 Mean Difference (I-J) -1.0800 1.4200 1.0800 2.5000* -1.4200 -2.5000* Std. Error .9485 .9485 .9485 .8659 .9485 .8659 Sig. .505 .318 .505 .027 .318 .027 95% Confidence Interval Lower Bound Upper Bound -3.5276 1.3676 -1.0276 3.8676 -1.3676 3.5276 .2657 4.7343 -3.8676 1.0276 -4.7343 -.2657 *. The mean difference is significant at the .05 level. a. Use the above output to report about the three pairwise comparisons: Does the confidence interval for 1 2 contain 0? ___Yes____ Does the confidence interval for 1 3 contain 0? ___Yes____ Does the confidence interval for 2 3 contain 0? ___No_...
View Full Document

Ask a homework question - tutors are online