SECTION 12.2 SUMMARY

• • The ANOVA F test does not say which of the group means differ. It is, therefore, usual to add comparisons among the means to basic ANOVA.

• • Specific questions formulated before examination of the data can be expressed as contrasts. Tests and confidence intervals for contrasts provide answers to these questions.

• • If no specific questions are formulated before examination of the data and the null hypothesis of equality of population means is rejected, multiple-comparisons methods are used to assess the statistical significance of the differences between pairs of means.

• • The power of the F test depends upon the sample sizes, the variation among population means, and the within-group standard deviation.