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Option Name
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Description
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Homogeneity of Variance
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Test
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specifies the type of
test to perform. Here are the valid values:
None
specifies that no test
is performed.
Bartlett
computes accurate Type
I error rates when the distribution of the data is normal.
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Test (continued)
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Brown & Forsythe
is a variation of
Levene's test. Equal variances are determined by using the absolute
deviations from the group medians. Although this is a good test for
determining variance differences, it can be resource intensive if
your data contains several large groups.
Levene
computes the squared
residuals to determine equal variance. Levene’s test is considered
to be the standard homogeneity of variance test. This is the default.
O’Brien
specifies O’Brien’s
test, which is a modification of Levene’s test that uses squared
residuals.
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Welch’s
variance-weighted ANOVA
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tests the group means
by using a weighted variance. You can use this test if the assumption
of equal variances is rejected.
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Comparisons
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You can select from
these comparison methods:
Bonferroni
performs Bonferroni t tests
of differences between means for all means of the main effect.
Duncan multiple range
performs Duncan’s
multiple range test on all means of the main effect.
Dunnett two-tail
performs Dunnett’s
two-tailed t test, testing whether any treatments
are significantly different from a single control for all main-effect
means.
Dunnett lower one-tail
performs Dunnett’s
one-tailed t test, testing whether any treatment
is significantly less than the control.
Dunnett upper one-tail
performs Dunnett’s
one-tailed t test, testing whether any treatment
is significantly greater than the control.
Gabriel
performs Gabriel’s
multiple-comparison procedure on all means of the main effect.
Nelson
analyzes all the differences
with the least squares means.
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Ryan-Einot-Gabriel-Welsch
performs the Ryan-Einot-Gabriel-Welsch
multiple range test on all means of the main effect.
Scheffé
performs Scheffé’s
multiple-comparison procedure on all means of the main effect.
Sidak
performs pairwise t tests
on differences between means with levels adjusted according to Sidak’s
inequality for all means of the main effect.
Student-Newman-Keuls
performs the Student-Newman-Keuls
multiple range test on all main effect means.
Least significant difference (LSD)
performs pairwise t tests
for all means of the main effect. In the case of equal cell sizes,
this test is equivalent to Fisher’s least significant difference
test.
Tukey
performs Tukey’s
studentized range test (HSD) on all means of the main effect. When
the group sizes are different, this is the Tukey-Kramer test.
You can also specify
the level of significance for the selected test.
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Plots
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By default, the results
include a box plot, a means plot, and a least squares mean difference
plot. You can also specify to include any diagnostic plots, which
can be displayed in a panel or as individual plots.
You can also specify
the maximum number of points to include in these plots.
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