Posted by
Rich Ulrich on
Jan 02, 2014; 7:56pm
URL: http://spssx-discussion.165.s1.nabble.com/One-Way-Anova-Repeated-Measures-Main-effect-is-significant-but-post-hoc-tests-are-not-significant-tp5723746p5723752.html
Bonferroni is an *alternate* way to test the whole
set of effects, so it is not unreasonable that it
might give different results. "There is an overall
difference; but none of the separate comparisons
meet a Bonferroni criterion, which is stiffer in
certain respects, though it might be more likely to
detect a single, extreme mean."
By the way, the "assumption of sphericity" is *not*
demonstrated by failing to reject at a 5% level, since
it happens to be a remarkably weak test in small samples.
If the p-value for that test is larger than 0.50 (not
0.05), then the sphericity is probably not a problem.
(Also, the Wikip article on Mauchly's suggests that the
test over-detects when Ns are large.)
- Yes, non-sphericity could contribute to non-significant
pair-wise testing, if the extreme groups have the larger
variances. How similar are the variances?
--
Rich Ulrich
----------------------------------------
> Date: Thu, 2 Jan 2014 08:35:45 -0800
> From:
[hidden email]
> Subject: One-Way Anova Repeated Measures: Main effect is significant, but post-hoc tests are not significant
> To:
[hidden email]
>
> Hi,
>
> I ran a one-way within-subjects ANOVA, with equal group sizes, and my data
> met the assumption of sphericity. I found a significant Main effect, but
> Bonferroni's tests did not reveal any significant post-hoc effects.
>
> Does anyone know why this might have happened? And how would I report this
> result?
>
> Thanks very much
>
>
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