Date:         Mon, 5 Sep 2005 15:19:24 -0400
Reply-To:     "Frank J. Gallo" <fjgallo@verizon.net>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         "Frank J. Gallo" <fjgallo@verizon.net>
Subject:      ANOVA and Post-hoc Tests
Content-Type: text/plain; charset="US-ASCII"

Hi All,



Looking for some help on interpreting contradictions found in an ANOVA run
with TukeyHSD follow-up. The F-test indicates significant differences among
groups.



ANOVA




Sum of Squares

df

Mean Square

F

Sig.



Between Groups
2.849

3

.950

2.830

.041



Within Groups
46.649

139

.336







Total
49.498

142













Levene = 5.168, p=.002, the null hypothesis that the error variance of the
dependent variable is equal across groups suggests no.

But, post-hoc comparisons show no significant differences among groups.

And, the homogenous subsets table identifies one set (4 groups, p=.143)
indicating that the means of the subgroups are not significantly different
from each other.



I do have unequal sample sizes: 23, 42, 30, 48. The run used the harmonic
mean (32.934), so I am aware that the Type 1 error level is not guaranteed.
Is this what I am seeing? That is, the p-value for the F-test is
underestimated and it should be larger. This is my first experience with
this kind of situation.



Yours thoughts are greatly appreciated.

Frank