the following is a more appropriate forum for your question, seeing as this has nothing to do with R (per se).
http://stats.stackexchange.com/questions good luck. peak99 wrote: > > Hello, > > I have some patient data for my masters thesis with three groups (n=16, 19 > & 20) > > I have completed compiling the results of 7 tests, for which one of these > tests the variances are unequal. > > > I wish to perform an ANOVA between the three groups but for the one test > with unequal variance (<0.001 by both bartlett and levene's test) I am not > sure what to do. > > I thought i would run ANOVA with bonferonni post-test for groups with > equal variances, then for the test with unequal variance i would use the > welch correction and games-howell post-test. Does this sound reasonable? > > Someone has also recommended to me to use Kruskal-wallis ANOVA, then use > Wilcoxon sign rank test pairwise to determine which groups are > significantly different (ON ALL DATA, both equal and unequal variance > tests). I don't think this is right, for two reasons: > > 1) Kruskal-wallis is for non-gaussian data, and i have no reason to > believe they are not normal. > - I have run normality tests which say they are normal, although > perhaps my sample sizes are too small for a normality test? > 2) i believe running pairwise Wilcoxon sign rank test is not acceptable > unless there is a post-test correction for multiple comparisons (i am not > aware of one); also on the wiki page for this test one of the assumptions > says "Under the null hypothesis the distributions of both groups are > equal" which i read to say that the variances must be equal. > > So I think there recommendations were based more on sample size and > normality, and not my issue with variance? > > > Ultimately i would like to know if i am going about this right with my > deduction (ANOVA/Bonferonni of the test results, but welch correction and > games-howell for the test with significantly different variances). and if > not why and/or what you think is a better option. > > most appreciated to any help received! > -- View this message in context: http://r.789695.n4.nabble.com/help-with-unequal-variances-tp3964779p3965046.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
