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From | Melaku Fekadu <melaku.fekadu@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: "dependent correlation" or c-statistics |
Date | Wed, 18 Aug 2010 17:01:14 +0300 |
Dear Mr. Roger, Thanks you. it was a great help. Melaku On Wed, Aug 18, 2010 at 4:04 PM, Roger Newson <r.newson@imperial.ac.uk> wrote: > It is probably not a good idea to choose a threshold according to whether > using that threshold gets a P-value of 0.05 or less. And it might not be a > good idea to use a threshold at all, as doing this implies that information > about trend within the 2 binary values is not used. > > To measure ordinal trend, without converting -ves- to binary, you might like > to use the -somersd- package, downloadable from SSC (or from my website if > you use Stata 9). If you install this package, then you can type > > somersd frailty ves, transf(z) tdist > > and you will compute a confidence interval for Somers' D of -ves- with > respect to -frailty-. And you can type > > somersd ves frailty, transf(z) tdist > > and compute a confidence interval for the Somers' D of -frailty- with > respect to -ves-. > > Alternatively, you can use the Harrell's c parameterization. Harrell's c is > linked to Somers' D by the relation D=2c-1, where D is Somers' D and c is > Harrell's c. To calculate a confidence interval and P-value for Harrell's c > of -ves- with respect to -frailty-, type > > > somersd frailty ves, transf(c) tdist > > and to calculate a confidence interval and a P-value for Harrell's c of > -frailty- with respect to -ves-, type > > somersd ves frailty, transf(c) tdist > > I hope this helps. > > Best wishes > > Roger > > > Roger B Newson BSc MSc DPhil > Lecturer in Medical Statistics > Respiratory Epidemiology and Public Health Group > National Heart and Lung Institute > Imperial College London > Royal Brompton Campus > Room 33, Emmanuel Kaye Building > 1B Manresa Road > London SW3 6LR > UNITED KINGDOM > Tel: +44 (0)20 7352 8121 ext 3381 > Fax: +44 (0)20 7351 8322 > Email: r.newson@imperial.ac.uk > Web page: http://www.imperial.ac.uk/nhli/r.newson/ > Departmental Web page: > http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/ > > Opinions expressed are those of the author, not of the institution. > > On 18/08/2010 12:34, Melaku Fekadu wrote: >> >> hello statalisters, >> >> i have two variables: one called 'ves' with values between 1 to 10, >> and the other is dichotomus called 'frality' with value either 0 or 1. >> >> i create a categorical variable from 'ves' 0-2 and 3-10 and make a >> chi-square test to test a relation with the variable frality, and i >> get p>0.05. But when i create another categorical variable of 'ves' >> with 0-4 and 5-10 and do the chi-square test i find that p<0.05. >> >> my question: what can i do to get a threshold value of 'ves' where >> p-value will be 0.05? somebody told me about a procedure calles >> "dependent correlation" or c-statistics in stata. >> >> any help will be appreciated. >> >> thanks >> * >> * 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/ > * * 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/