LISTSERV at the University of Georgia
Menubar Imagemap
Home Browse Manage Request Manuals Register
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (September 2003)Back to main SPSSX-L pageJoin or leave SPSSX-L (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Tue, 2 Sep 2003 10:19:04 +0200
Reply-To:     Asesoría Bioestadística
              <bioestadistica@eresmas.net>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Asesoría Bioestadística
              <bioestadistica@eresmas.net>
Subject:      Re: ANOVA or Kruskal-Wallis ANOVA
Content-Type: text/plain; charset=us-ascii

> 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 Kolmogorov-Smirnov > Test?

Montecarlo simulations have shown that Shapiro-Wilk test is better than K-S(Lilliefors).

> 2) So within each group, the p-value 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 Brown-Forsythe 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 p-value 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 p-values 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 Garcia-Granero


Back to: Top of message | Previous page | Main SPSSX-L page