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From |
"FEIVESON, ALAN H. (AL) (JSC-SK) (NASA)" <alan.h.feiveson@nasa.gov> |

To |
"'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: ANOVA Multiple Comparison Questions |

Date |
Fri, 5 Mar 2004 12:41:24 -0600 |

There is a method of doing multiple comparisons aftter a KW test. I don't have the original source, but there is a website from P. Cabillo and J. Masaro that describes the procedure. See http://ace.acadiau.ca/math/cabilio/StatLabs/BSPT(02).pdf p. 27 Al Feiveson -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of gte573q@mail.gatech.edu Sent: Friday, March 05, 2004 12:20 PM To: statalist@hsphsun2.harvard.edu Subject: st: ANOVA Multiple Comparison Questions Hi! I have a question about ANOVA. I'd like to see the differences of per capita income(index) for four different areas. I chose oneway ANOVA and multiple comparison command. But the problem is the violation of equal variances (please refer to Bartlett's test for equal variances below). My questions are: 1) Can I say that my analysis is valid under the violation of equal variances? 2) If the violation of equal variances is a problem, is there any way to get over it? 3) As an alternative, I tried to nonparametic test using Kruskal-Wallis test. But "Kwallis" command does not produce multiple comparison for each group. Is there any nonparametric ANOVA techniques with multiple comparison? 4) I think this data is unbalanced in terms of # of observation. Is this problem? Any comments would be helpful to me. Thanks. sugie -------------------------------------------------------------- .oneway pci_index group [aweight=population], tabulate scheffe | Summary of pcir0 group | Mean Std. Dev. Freq. Obs. ------------+------------------------------------------------ A | 1.2176654 .73457797 127574 47 B | .76321118 .43276015 2778506 845 C | 1.0260904 .48150203 2989897 767 D | 1.0885976 .37953544 6232038 1160 ------------+------------------------------------------------ Total | 1.0000001 .44391706 12128015 2819 Analysis of Variance Source SS df MS F Prob > F ------------------------------------------------------------------------ Between groups 49.4593539 3 16.4864513 91.74 0.0000 Within groups 505.862359 2815 .179702437 ------------------------------------------------------------------------ Total 555.321713 2818 .197062354 Bartlett's test for equal variances: chi2(3) = 41.7568 Prob>chi2 = 0.000 Comparison of pcir0 by class (Scheffe) Row Mean-| Col Mean | A B C ---------+--------------------------------- B | -.454454 | 0.000 | C | -.191575 .262879 | 0.029 0.000 | D | -.129068 .325386 .062507 | 0.242 0.000 0.018 .kwallis pci_index, by(group) Test: Equality of populations (Kruskal-Wallis test) +--------------------------+ | group | Obs | Rank Sum | |-------+------+-----------| | A | 47 | 64350.00 | | B | 845 | 801156.00 | | C | 767 | 1.14e+06 | | D | 1160 | 1.97e+06 | +--------------------------+ chi-squared = 423.506 with 3 d.f. probability = 0.0001 chi-squared with ties = 423.506 with 3 d.f. probability = 0.0001 . * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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