Date: Tue, 2 Sep 2003 10:19:04 +0200
ReplyTo: Asesoría Bioestadística
<bioestadistica@eresmas.net>
Sender: "SPSSX(r) Discussion" <SPSSXL@LISTSERV.UGA.EDU>
From: Asesoría Bioestadística
<bioestadistica@eresmas.net>
Subject: Re: ANOVA or KruskalWallis ANOVA
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> Marta, in response to your questions about:
>
>  Every sample size (not just the total sample size)
>  Skewness/Kurtosis for every sample
>
> Here it is:
>
> Group A (n=17) Mean= 8.76 (SD=4.42) Min, Max (2,16)
> Skewness= 0.087 (SE=0.550) Kurtosis =1.256 (SE=1.06)
> Normality: Shapiro Wilk .937, df=17, p=0.281
>
> Group B (n=22) = 5.50 (SD=2.60) Min, Max (1,12)
> Skewness= 0.611 (SE=0.491) Kurtosis =0.649 (SE=0.95)
> Normality: Shapiro Wilk .957, df=22, p=0.425
>
> Group C (n=8) Mean=6.50 (SD=4.24) Min, Max 0 12
> Skewness= 0.539 (SE=0.752) Kurtosis =0.863 (SE=1.48)
> Normality: Shapiro Wilk .937, df=8, p=0.580
>
> Group D (n=26) Mean=5.08 (SD=3.10) Min, Max 1,12
> Skewness= 0.613 (SE=0.456) Kurtosis =0.203 (SE=0.887)
> Normality: Shapiro Wilk .934, df=26 p=0.099
>
> 1) By the way, what is the difference between Shapiro Wilk & the KolmogorovSmirnov
> Test?
Montecarlo simulations have shown that ShapiroWilk test is better than KS(Lilliefors).
> 2) So within each group, the pvalue is not significant for the normality test so the
> hypothesis of normality cannot be rejected
>
> 3) Levene Test 3.17, df1=3, df2=69, p=0.030
> > Homogeneity of variances was rejected
>
> So  do you think a case can be made using ANOVA and then the Tamhane test?
Yes, use Welch or BrownForsythe test (if you have SPSS11.x) instead of ordinary ANOVA.
Remember that Tamhane test is highly conservative. If you want something more sensitive
use contrasts and decide which pvalue adjustment you are going to use.
This is the coefficient matrix for the contrasts:
1 1 0 0
1 0 1 0
1 0 0 1
0 1 1 0
0 1 0 1
0 0 1 1
> Also  when I ran this, the pvalues the output provides are not adjusted for multiple
> comparisons, correct?
Are you talking about Tamhane test. It is already adjusted (and heavily, too). Only
contrasts are not adjusted in any way.
Regards
Marta GarciaGranero
