Hello, I am running polychoric correlations on a dataset composed of 12 ordinal and binary variables (N =384), using the polycor package. One of the association (between 2 dichotomous variables) is very high using the 2-step estimate (0.933 when polychoric run only between the two variables; but 0.801 when polychoric run on the 12 variables). The same correlation run with ML estimate returns a singularity message.
First, I would like to know why the estimations between only the two dichotomous variables and with all the variables at once (with the 2-step estimate) returns slightly different results. Secondly, when i checked back the distribution of these two dichotomous variables they appear about symmetrically opposed. Therefore, one should indeed expect a strong association between them, but a negative one, isn't it? Why does the polychoric correlation returns a positive coefficient? What does it mean for the rest of the coefficients, should i trust them? I have to say I'm new to R and not very strong in statistics, I hope I haven't posted a stupid question... cheers, Dorothee -- View this message in context: http://www.nabble.com/polychoric-correlation%3A-issue-with-coefficient-sign-tp21425977p21425977.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
