Re: [R] polychoric correlation: issue with coefficient sign

2009-01-14 Thread Dorothee
Dear John and Stas, Thanks so much for your help. John, I did the correlation on the complete dataset (no missing values). I tried what you suggested and you were right: hetcor with pd=FALSE gives me the same result as polychor. Anyway, thanks to the answers I got in the forum, I understand I sho

Re: [R] polychoric correlation: issue with coefficient sign

2009-01-13 Thread Stas Kolenikov
The original Olsson's paper (http://www.citeulike.org/user/ctacmo/article/553309) did mention that the greatest biases and numeric problems were encountered when the two variables had opposite skewness. Your example is even more extreme: tetrachoric and polychoric correlations do not like zero coun

Re: [R] polychoric correlation: issue with coefficient sign

2009-01-13 Thread John Fox
Dear Dorothee, > -Original Message- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf Of Dorothee > Sent: January-13-09 8:49 PM > To: r-help@r-project.org > Subject: Re: [R] polychoric correlation: issue with coefficient sign > &

Re: [R] polychoric correlation: issue with coefficient sign

2009-01-13 Thread Dorothee
Thank you so much for all your answers! And sorry for being scarce on the details. My dataset has 12 variables (6 ordinal coded from 1 to 5, and 6 binary) and 384 cases without missing value. High values mean 'positive' attitude toward the object of study. I probably went too fast in my earlier i

Re: [R] polychoric correlation: issue with coefficient sign

2009-01-13 Thread John Fox
Dear Jim and Dorothee, > -Original Message- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf Of Jim Lemon > Sent: January-13-09 5:17 AM > To: Dorothee > Cc: r-help@r-project.org > Subject: Re: [R] polychoric correlation: issue

Re: [R] polychoric correlation: issue with coefficient sign

2009-01-13 Thread Jim Lemon
Dorothee wrote: 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 tw

[R] polychoric correlation: issue with coefficient sign

2009-01-12 Thread Dorothee
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