Rafa Braga asked > > Does anybody know how to detect association between two traits while removing > the influence of the third one? I have three traits which are named a b and > c. I'm wanting to test the correlation of a and b while controling c as a > covariate. In other words, the correlation between trait a and b can be a > result of the correlation between b and c and I'm wanting to remove the > influence of c on b.
This goes all the way back 100 years. Once you have inferred the variances and covariances of the three traits, you can compute the partial correlation between a and b. This is defined as the correlation between the residual of a when predicted by c, and the residual of b when predicted by c. When there is only one variable c, and when r(a,b) is the correlation of a with b, then the partial correlation is [ r(a,b) - r(a,c) r(b,c)] / [(sqrt(1 - r(a,c)^2) sqrt(1 - r(b,c)^2)] For likelihood ratio testing in a linear model, one could compare the likelihoods of models that did or did not have direct connection of a and b. RA Fisher also derived a distribution of the partial correlation coefficient. Joe ---- Joe Felsenstein j...@gs.washington.edu Department of Genome Sciences and Department of Biology, University of Washington, Box 355065, Seattle, WA 98195-5065 USA > > > > Yours, > Rafa > > [[alternative HTML version deleted]] > > _______________________________________________ > R-sig-phylo mailing list - R-sig-phylo@r-project.org > https://stat.ethz.ch/mailman/listinfo/r-sig-phylo > Searchable archive at http://www.mail-archive.com/r-sig-phylo@r-project.org/ -- ---- Joe Felsenstein j...@gs.washington.edu Department of Genome Sciences and Department of Biology, University of Washington, Box 355065, Seattle, WA 98195-5065 USA _______________________________________________ R-sig-phylo mailing list - R-sig-phylo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-phylo Searchable archive at http://www.mail-archive.com/r-sig-phylo@r-project.org/
