Statistical Methods in Medical Research 4ed

Table 9.4 Clotting time (min) of plasma from three subjects, three methods of treatment and three
replications of each subject±treatment combination.
Treatment
Subject 2 3 4 Total
6 9 8 9 9 11 3
10 1 9 5 10 7
9 8 10 0 10 7
T11 29 7 29 4 32 7 R1 91 8
S11 294 09 288 26 356 67
7 9 2 9 1 10 3
8 6 9 1 10 7
9 2 9 4 10 2
27 0 27 6 31 2 R2 85 8
243 24 253 98 324 62
8 8 4 8 6 9 8
7 9 8 0 10 1
8 0 8 0 10 1
24 3 24 6 30 0 R3 78 9
196 97 201 96 300 06
Total C1 81 0 C2 81 6 C3 93 9 T 256 5
P y 2 2459 85
CT ˆ T 2 =27 ˆ 2436 75
Subjects SSq ˆ‰…91 8† 2 ‡ ...‡…78 9† 2 Š=9 CT ˆ 9 2600
Treatments SSq ˆ‰…81 0† 2 ‡ ...‡…93 9† 2 Š=9 CT ˆ 11 7800
Interaction SSq ˆ‰…29 7† 2 ‡ ...‡…30 0† 2 Š=3 CT Subj: SSq Treat:SSq ˆ 0 7400
Total SSq ˆ…9 8† 2 ‡ ...‡…10 1† 2 CT ˆ 2459 85 CT ˆ 23 1000
Residual SSq ˆ Total Subjects Treatments Interaction ˆ 1 3200
Analysis of variance
SSq DF MSq VR
Subjects 9 2600 2 4 6300 63 1
Treatments 11 7800 2 5 8900 80 3
Interaction 0 7400 4 0 1850 2 52 (P ˆ 0 077)
Residual 1 3200 18 0 0733 1 00
Total 23 1000 26
9.2 Two-way analysis of variance: randomized blocks 245
The interpretation of significant interactions and the interpretation of the
tests for the `main effects' (subjects and treatments in Examples 9.1 and 9.2)
when interactions are present will be discussed in the next section.