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In-Depth Information
One-Way Analysis of Variance
Results
The ANOVA Procedure
Levene ' s Test for Homogeneity of GAFscore Variance
ANOVA of Squared Deviations from Group Means
Sum of
Squares
Mean
Square
Source
therapy
Error
DF
F Value
Pr
>
F
2
12
11603.1
19775.9
5801.6
1648.0
3.52
0.0627
Levene's test indicated
that the variances are
not significantly
different; the
probability is > .05.
Brown and Forsythe ' s Test for Homogeneity of GAFscore Variance
ANOVA of Absolute Deviations from Group Medians
Sum of
Squares
Mean
Square
Source
therapy
Error
DF
F Value
Pr
>
F
2
12
113.7
159.6
56.8667
13.3000
4.28
0.0396
Bartlett ' s Test for Homogeneity of
GAFscore Variance
Source
therapy
DF
Chi-Square
Pr
>
ChiSq
There are unequal variances across
levels of the independent variable;
the probability is < .05.
2
10.2938
0.0058
Welch ' s ANOVA for GAFscore
Source
therapy
Error
F Value
DF
Pr > F
2.0000
5.5191
24.10
0.0019
Figure 5.40
Tests of homogeneity of variance.
TheWelchresultsareshowninthebottomportionofFigure5.40.As
canbeseeninthecolumnlabeled Fvalue , the obtained value is 24.10,
the same value yielded by SPSS (see Figure 5.20). The probability of this
value occurring by chance is .0019. This result is statistically significant
(our alpha level is .05), and, as we will see in Chapter 6, indicates that we
have reliable group mean differences.
5.7 COMMUNICATING THE RESULTS
Before proceeding with the data analysis, we examined all variables for pos-
sible code and statistical assumption violations, as well as for missing values,
and outliers, with SPSS Frequencies, Explore, and One-Way ANOVA proce-
dures. The fifteen mental health consumers had no missing values on the one
continuous dependent measure, GAF.
Several univariate outliers were detected, none of which were considered
extreme or unusual enough to require deletion. Because there was random
assignment of participants to treatment conditions and random selection
of participants from the population as a whole, we deemed independence
 
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