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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

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

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

Date |
Sat, 29 Nov 2003 11:35:31 -0000 |

-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/

**References**:**st: What does contribution to chi-square mean in tabchii***From:*"Donald Spady" <dspady@ualberta.ca>

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