Date: Mon, 5 Sep 2005 22:21:45 -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: Re: ANOVA and Post-hoc Tests
In-Reply-To: <015e01c5b27d$38aa7b00$63076cc8@datatrend>
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Hi Isacc,
Fisher's LSD test does not correct for multiple comparisons as the Tukey HSD
post test does. Tukey HSD sets the 5% significance level for the entire
family of comparisons. Generally, researchers do not recommend Fisher's LSD
test but Tukey's HSD. This is my understanding.
Thanks,
Frank
-----Original Message-----
From: Isaac Dialsingh [mailto:consult@tstt.net.tt]
Sent: Monday, September 05, 2005 8:51 PM
To: Frank J. Gallo
Subject: Re: ANOVA and Post-hoc Tests
Why didn't you use the LSD test?
Isaac
----- Original Message -----
From: "Frank J. Gallo" <fjgallo@verizon.net>
Newsgroups: bit.listserv.spssx-l
To: <SPSSX-L@LISTSERV.UGA.EDU>
Sent: Monday, September 05, 2005 3:19 PM
Subject: ANOVA and Post-hoc Tests
> 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
