Chapter 5, Table 4: Comparisons/Contrasts via SPSS Syntax

The following data consists of blood pressure measurements for six individuals randomly assigned to one of four groups. Our purpose here is to perform four planed contrasts in order to discern if group differences exist for the selected contrasts of interests.

1. Comparisons/contrasts are performed by syntax within the ONEWAY ANOVA procedure. By default, procedures for homogeneity of variance assumed and homogeneity of variance not assumed are carried out.

At this point, clicking Run and then All is necessary in order to obtain the results.

* Note that using the /POSTHOC option allows one to form confidence intervals using a variety of critical values. However, the confidence intervals formed are for all pairwise comparisons, which may not be of interest for a particular question. For example, the question of interest in the present situation involved three pairwise comparisons and one complex comparison, for a total of four confidence intervals. The critical value using the Bonferroni criterion should then be alpha divided by 4. However, by performing the Bonferroni procedure via the Post Hoc procedure the alpha is divided by six, as there are six possible pairwise comparisons for four groups. In addition, the Post Hoc procedure is limited to pairwise comparisons and thus does not form confidence intervals for complex comparisons.