Appendix C. Basic ANOVA Concepts
C.1 Within- vs. Between-Group Variation 447
C.2 Noise Reduction by Blocking 449
C.3 Least Squares Mean (LS-mean) 453
C.1 Within- vs. Between-Group Variation
Suppose 12 recent college graduates are assigned to three groups: 4 subjects to an exercise group (I), 4 subjects to a drug treatment group (II), and 4 subjects to a control group (III). Ages, pulse rates, diastolic blood pressures, and triglyceride measurements are taken after 8 weeks in the study, with the following results:
The age measurements are the same for all 12 subjects. Clearly, there is no variation among the group means and, therefore, no difference among groups with respect to age.
Pulse Rates (beats/min.)
The pulse rate measurements are the ...