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From |
Steven Samuels <sjhsamuels@earthlink.net> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: Pearson chi square and Rao and Scott correction validity |

Date |
Thu, 6 Nov 2008 17:04:00 -0500 |

-Steve On Nov 6, 2008, at 7:33 AM, Nick Cox wrote:

There is no need to invoke belief! My -tabchi- and -tabchii-(programs) from the -tab_chi- package on SSC do indeed givewarnings. (There is no Stata program called tab-chi.)But these old warnings are very conservative. Many writers nowadvise that chi-square works fine so long as all expectedfrequencies are above about 1. In any case, the point can beexplored by simulations or bootstrapping. Often it is better to useFisher's exact test.I can't advise on the main issue, which is for svy-savvy people,but in general very low expected frequencies could be problematicfor any method.Nick n.j.cox@durham.ac.uk Ángel Rodríguez Laso I've been reviewing the manuals and statalist archives and I've confirmed that Stata does not give any automatic warning message when requirements for a valid chi-square test are not met (i.e. no more than 20% of the expected values in a table are less than 5 and none are less than 1), what I think is a nuisance. I suppose this can be only worked out by writing the option 'expected' after tabulate and checking oneself if the requirements are met. I believe Cox's tab-chi package does give a warning when requirements are not met. I wonder also if the Rao and Scott correction of Pearson chi-square that is recommended for survey designs needs the same requirements. The problem then would be that -svy:tab- doesn't support the 'expected' option neither tab-chi is suitable for survey analysis. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: Pearson chi square and Rao and Scott correction validity***From:*"Ángel Rodríguez Laso" <angelrlaso@gmail.com>

**st: RE: Pearson chi square and Rao and Scott correction validity***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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