Page 198 - Intermediate Statistics for Dummies
P. 198

16_045206 ch10.qxd  2/1/07  10:14 AM  Page 177
                                                                        Chapter 10
                                                   Pairing Things Down with
                                         In This Chapter
                                           When and how to follow up ANOVA with multiple comparisons
                                           Comparing two well-known multiple comparison procedures
                                                    Y  Multiple Comparisons
                                                        ou’re comparing the means of not two, but k independent populations,
                                                        and you find out (using ANOVA — see Chapter 9) that you reject Ho: All
                                                    the population means are equal, and you conclude Ha: At least two of the
                                                    population means are different. Now you gotta know — which of those popu-
                                                    lations are different? Answering this question requires a follow-up procedure
                                                    to ANOVA called multiple comparisons, which makes sense because you want
                                                    to compare the multiple means you have and see which ones are different.
                                                    In this chapter, you figure out when you need to use a multiple comparison
                                                    procedure. You see two of the most well-known multiple comparison proce-
                                                    dures: Fisher’s LSD (least significant difference) and Tukey’s test. They can
                                                    help you answer that burning question: So some of the means are different,
                                                    but which ones are different?


                                         Following Up after ANOVA



                                                    This section runs through the ANOVA procedure in the case where Ho is
                                                    rejected and leads you to the next step: multiple comparisons.

                                                    Suppose you want to compare the average number of cell-phone minutes
                                                    used per month for children and young adults, where the age groups are the
                                                    following:
                                                       Group 1: 19 years old and under
                                                       Group 2: 20-39 years old
   193   194   195   196   197   198   199   200   201   202   203