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Y603 Lectures
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Lecture #28
1. Continued with one-way analysis
of covariance (ANCOVA)
Can interpret results from SAS
printouts based on one-way ANCOVA
Test the linearity assumption between the
covariate and the dependent variable by plotting the data for each
treatment group and examining the slop by an F-test which is the
test of b
w1, b
w2, and b
w3 , etc.
Test the equal-slop assumption with an
interaction term (i.e., X*TREAT) in the MODEL statement in
SAS.
Concepts from SAS printout: LSMEANS, STDERR, PDIFF
Terms to learn: adjusted means, post-hoc comparisons of
adjusted means
Logic behind the analysis of covariance
Kirk's notations used for two-way ANCOVA
2. Assignments:
(1) Continue to review Sections
15.1-15.4 in Kirk.
(2) Do problems 2, 7, 8, 9(a), 9(b),
9(d), 10(a), 10(b), and 10(d) of Chapter 15 in Kirk.
(3) Preview Section 15.9 in
Kirk.
Read the following articles on
ANCOVA--
Porter, A. C. and Raudenbush, S.
W. (1987). Analysis of covariance: Its model and use in
psychological research. Journal of Counseling
Psychology, 34(4), 383-392.
Maxwell, S. E. Delaney, H. D. and
Dill, C. A. (1984). Another look at ANCOVA versus blocking.
Psychological Bulletin, 95(1),
136-147.
Jennings, E. (198?). Analysis of
covariance with nonparallel regression lines. Journal of
Experimental Education, ?, 129-134.
Harwell, M. (1997). An
investigation of the effect of nonlinearity of regression on
the ANCOVA F-test. Paper presented at the annual meeting of
the American Educational Research Association, Chicago,
Illinois.
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