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Example 16
Testing Model D against Model C gives a chi-square value of 1.179 (= 3.976 – 2.797)
with 1 (that is, 5 – 4) degree of freedom. Again, you would accept the hypothesis of
equal regression weights (Model D).
With equal regression weights, the comparison of treated and untreated subjects
now turns on the difference between their intercepts. Here are the parameter estimates
for the 105 control subjects:
The estimates for the 108 experimental subjects are:
The intercept for the experimental group is estimated as 3.63. According to the text
output (not shown here), the estimate of 3.63 has a critical ratio of 7.59. Thus, the
0, 29.51
pre_verbal
18.62
pre_syn
0, 9.49
eps1
1.00
1
19.91
pre_opp
0, 11.92
eps2
.88
1
0
post_verbal
20.38
post_syn
0, 5.78
eps3
21.20
post_opp
0, 12.38
eps4
1.00
1
.91
1
.90
0, 1.02
zeta
1
Example 16: Model D
An alternative to ANCOVA
Olsson (1973): control condition.
Unstandardized estimates
6.33
1.88, 46.90
pre_verbal
18.62
pre_syn
0, 2.52
eps1
1.00
1
19.91
pre_opp
0, 12.25
eps2
.88
1
3.63
post_verbal
20.38
post_syn
0, 7.38
eps3
21.20
post_opp
0, 17.05
eps4
1.00
1
.91
1
.90
0, 8.74
zeta
1
Example 16: Model D
An alternative to ANCOVA
Olsson (1973): experimental condition.
Unstandardized estimates
7.24