Note: varð^b 1 þ^b 3 Þ¼varð^b 1 Þþvarð^b 3 Þþ 2 covðb^ 1 ;^b 3 Þ.
See Chap. 5.- The working covariance matrix pertains to the covari-
ance between responses from the same cluster. The
covariance matrix for parameter estimates pertains to
the covariance between parameter estimates. - Wald test:H 0 :b 3 ¼0 for Model 1
Test statistic:z^2 ¼(0.2136/ 0.7993)^2 ¼0.069;
P-value¼0.79
Conclusion: do not rejectH 0. - Score test:H 0 :b 3 ¼0 for Model 1
Test statistic¼0.07 test statistic distributedw^2 1df
P-value¼0.79
Conclusion: do not rejectH 0. - dORðfrom Model 2 Þ:expð 0 : 3104 Þ¼ 1 : 36 ;
dORðfrom Model 3 Þ:expð 0 : 3008 Þ¼ 1 : 35 :
The odds ratios for RX are essentially the same
whether SEQUENCE is or is not in the model, indicat-
ing that SEQUENCE is not a confounding variable by
the data-based approach. From a theoretical perspec-
tive, SEQUENCE should not confound the association
between RX and heartburn relief because the distri-
bution of RX does not differ for SEQUENCE¼ 1
compared to SEQUENCE¼0. For a given patient’s
sequence, there is one observation where RX¼1, and
one observation where RX¼0. Thus, SEQUENCE
does not meet a criterion for confounding in that it is
not associated with exposure status (i.e., RX).
Chapter 16 True-False Questions:
- F: a marginal model does not include a subject-
specific effect - T
- T
- T
- T
- logitmi¼b 0 þb 1 RXiþb 2 SEQUENCEi
þb 3 RXiSEQiþb 0 i - dORðwhereSEQUENCE¼ 0 Þ¼expð 0 : 4707 Þ¼ 1 : 60
dORðwhereSEQUENCE¼ 1 Þ¼expð 0 : 4707 0 : 2371 Þ¼ 1 : 26 - dOR¼expð 0 : 3553 Þ¼ 1 : 43
95 %CI:exp½ 0 : 3553 1 : 96 ð 0 : 4565 Þ¼ð 0 : 58 ; 3 : 49 Þ - The interpretation of the odds ratio, exp(b 1 ), using the
model for this exercise is that it is the ratio of the odds
for an individual (RX¼1 vs. RX¼0). The interpreta-
tion of the odds ratio for using a corresponding GEE
688 Test Answers