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From |
"Donald Spady" <dspady@ualberta.ca> |

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

Subject |
st: Re: RE: What does contribution to chi-square mean in tabchii |

Date |
Mon, 1 Dec 2003 09:53:35 -0700 |

Thanks for the response. I will use it as a way to get insight into the data, but for little else. Don ----- Original Message ----- From: "Nick Cox" <n.j.cox@durham.ac.uk> To: <statalist@hsphsun2.harvard.edu> Sent: Saturday, November 29, 2003 4:35 AM Subject: st: RE: What does contribution to chi-square mean in tabchii > -tabchii- is a user-written command. A version > which will work in Stata 6 through 8 is > available from the -tab_chi- package on SSC > and an earlier version which will work in > Stata 5 is available from > http://www.stata.com/users/njc/tab_chi/ > > I am not sure what kind of answer Don > wants here. The definition of contribution > given in the help file is > > (observed frequency - expected frequency)^2 > / expected frequency > > and Don clearly understands that. The > programmer's intent in allowing > such contributions to be shown was that > some users like to see that step, perhaps > even as a check on hand calculations. > Personally I much prefer to look at > the (signed) square root of that > > (observed freq - expected freq) > / sqrt(expected frequency) > > given the usual argument that the direction of > deviation from expectation is often helpful > in interpretation. These quantities are called Pearson > residuals in -tabchii- and indeed > elsewhere. And in turn a refinement > on that, the adjusted residual, > has a distribution in the null case > that is closer to Gaussian(0,1). > > Nick > n.j.cox@durham.ac.uk > > Donald Spady > > > Can you please tell me how to interpret the chi-square > > 'contribution' to > > chi-sqare as used in tabchii. I find it useful in telling > > me where the > > total chi-square is coming from but is there more that one > > can get out of > > it? i.e. say the chi-square (total) is 100 and the > > contribution of one cell > > is 55, another is 35, another 5 and another 5. Obviously > > the first cell's > > chi square counts a lot but can I say anything else, say in > > regard to cell > > 2's chi-square of 35. Or is it just an interesting way of > > getting an > > insight into the data. > > * > * 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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