Information Technology Reference
In-Depth Information
Figure 7.1
The general
Post Hoc
dialog window in SPSS.
the
Hochberg GT2
and
Gabriel
tests, which are based on this latter dis-
tribution, can work with unequal sized groups; the
Duncan,
S-N-K, and
the two Tukey tests available in SPSS were designed to apply to groups of
equal size, at least in hand calculations.
7.8.2.4
F
Statistic
It is also possible to use an
F
statistic to compare mean differences. Kirk
(1995, p. 125) tells us, though, that with the groups having equal sample
sizes,
t, q,
and
F
are related to each other as follows.
√
F
q
√
2
=
t
=
.
(7.4)
7.8.3 A ROUGH GROUPING OF THE TESTS
The post hoc tests that are available in SPSS (SAS has a subset of these)
are shown in Figure 7.1; this is SPSS's
Post Hoc
dialog window. They
are conveniently divided into two sets, those assuming equal group or
population variances (homogeneity of variance) in the top panel and
those not requiring that assumption to be met in the bottom panel. Not
that we would recommend the practice but you can select as many as you
wish in any one analysis, although with many groups and many tests the
output can become quite lengthy.
