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From |
Marcos Vinicius <bioestatistico@inbox.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Can Spearman's rho be used to measure of the degree of association between two binary variables ? |

Date |
Mon, 21 May 2012 08:55:00 -0800 |

Hello, Thank you everyone for the replies. I am a luck person participating in this group with brilhant minds. ..Always inspiring and incentivating me in this fields of biostatistics. Have a nice week, MArcos Vinicius. > -----Original Message----- > From: dirk.enzmann@uni-hamburg.de > Sent: Mon, 21 May 2012 15:47:44 +0200 > To: statalist@hsphsun2.harvard.edu > Subject: Re: st: Can Spearman's rho be used to measure of the degree of > association between two binary variables ? > > Marcos Vinicius asked, whether Spearman's rho can be used to measure the > degree of association between two binary variables, see: > > http://www.hsph.harvard.edu/cgi-bin/lwgate/STATALIST/archives/statalist.1205/date/article-836.html > > to which he received very helpful answers (perhaps more than he > initially wanted to know): > > - from Maarten Buis and Richard Williams > http://www.hsph.harvard.edu/cgi-bin/lwgate/STATALIST/archives/statalist.1205/date/article-855.html > http://www.hsph.harvard.edu/cgi-bin/lwgate/STATALIST/archives/statalist.1205/date/article-859.html > who discuss whether multicollinearity should be regarded as a problem at > all > > - and from Cameron McIntosh, Richard Stoll, and Roger Newson > http://www.hsph.harvard.edu/cgi-bin/lwgate/STATALIST/archives/statalist.1205/date/article-837.html > http://www.hsph.harvard.edu/cgi-bin/lwgate/STATALIST/archives/statalist.1205/date/article-838.html > http://www.hsph.harvard.edu/cgi-bin/lwgate/STATALIST/archives/statalist.1205/date/article-858.html > who point at alternative measures for the association of two binary > variables. > > Let me add two comments as to the use of tetrachoric (or polychoric) > correlation coefficients vs. Pearson (or Spearman) correlation > coefficients in the case of two binary variables: > 1) Tetrachoric and Pearson correlations answer different questions: The > first estimates the correlation of two *latent* (quasi-continuous) > variables "behind" the observed dichotomous variables, thus assuming > that both variables are artificially dichotomous, whereas the Pearson > coefficients shows how the *observed* values correlate, thus assuming > naturally dichotomous variables. > 2) Ledesma et al. (2011) (see: > http://openjournal.konradlorenz.edu.co/index.php/rlpsi/article/viewFile/459/463 > ) cited by Cameron write: "Stata gives their users a function based on a > work by Edwards and Edwards (1984), that is basically 'a very rough > approximation' and > is consequently unsuitable for many applications ..." (p. 182). This is > not quite correct: Stata computes the tetrachoric correlation "... by > using the Edwards and Edwards (1984) noniterative estimator as the > *initial* value" (see: [R] Base Referencence, p. 2196; bold face by me) > - the coefficient calculated by Stata is at least as precise as the > coefficient calculated by Ledesma et al.'s Vista-Tetrachor program: > > * --- Example from Ledesma et al., p. 183 ------------------------ > input y x ncases > 1 1 203 > 1 0 186 > 0 1 167 > 0 0 374 > end > expand ncases > tetrachoric x y > * --- End of Stata example --------------------------------------- > > Dirk > > ======================================== > Dr. Dirk Enzmann > Institute of Criminal Sciences > Dept. of Criminology > Rothenbaumchaussee 33 > D-20148 Hamburg > Germany > > phone: +49-(0)40-42838.7498 (office) > +49-(0)40-42838.4591 (Mrs Billon) > fax: +49-(0)40-42838.2344 > email: dirk.enzmann@uni-hamburg.de > http://www2.jura.uni-hamburg.de/instkrim/kriminologie/Mitarbeiter/Enzmann/Enzmann.html > ======================================== > * > * 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/ ____________________________________________________________ FREE 3D EARTH SCREENSAVER - Watch the Earth right on your desktop! Check it out at http://www.inbox.com/earth * * 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**:**Re: st: Can Spearman's rho be used to measure of the degree of association between two binary variables ?***From:*Dirk Enzmann <dirk.enzmann@uni-hamburg.de>

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