search for: tetrachoric

Hi, Is there any R library/package that calculates tetrachoric correlations from given marginals and Pearson correlations among ordinal variables? Inputs to polychor function in polycor package are either contingency tables or ordinal data themselves. I am looking for something that takes marginal distributions and Pearson correlation as inputs. For example...

I hope someone here knows the answer to this since it will save me from delving deep into documentation. Based on 22 pairs of vectors, I have noticed that tetrachoric correlation coefficients in stata are almost uniformly higher than those in R, sometimes dramatically so (TCC=.61 in stata, .51 in R; .51 in stata, .39 in R). Stata's estimate is higher than R's in 20 out of 22 computations, although the estimates always fall within the 95% CI for th...

About two years ago there was a thread about this which suggested that at that time nobody had these coefficients ready to go. (a) has anyone in the meanwhile programmed them? (b) I think I can see how to do the tetrachoric one with mvtnorm on similar lines to an example on the help page so will try that if nobody else already has (c) looking at the polychoric one makes me realise yet again that I wish I knew more mathematics. I would also find it difficult to test it as I do not have any worked examples. Does any...

Hi there, Am I correct to believe that tetrachoric correlation is a special case of polychoric correlation when there are only two levels to the ordered factor? Thus it should be okay to use hetcor from the polycor package to build a matrix of correlations for binary variables? If this is true, how can one estimate 95% confidence intervals for...

A bit late, but you might like to look at http://www.qimr.edu.au/davidD/polyr.R Regarding the original posters queries: You can analyse polychoric correlations as if they were Pearson correlations using standard software (eg sem), and this usually doesn't do too badly, or go to AWLS (Browne) in LISREL etc, or ML analysis of the full multidimensional contingency table using programs such as

Haj i try to perform a principal component analysis by using a tetrachoric correlation matrix as data input tetra <- tetrachoric (image_na, correct=TRUE) t_matrix <- tetra$rho pca.tetra <- principal(t_matrix, nfactors = 10, n.obs = nrow(image_na), rotate="varimax", scores=TRUE) the problem i have is to compute the individual factor scores from the pca...

Suppose F(x, y; rho) is the cdf of a bivariate normal distribution, with standardized marginals and correlation parameter rho. For any fixed x and y, I wonder if F(x, y; rho) is a monotone increasing function of rho, i.e., there is a 1 to 1 map from rho to F(x, y; rho). I explored it using the function pmvnorm in package mvtnorm with different x and y. The plot suggests the statement may be true.

...fit.dat <- cfa(model.1, data=my.dat, std.lv = T, estimator="WLSMV", ordered=c("var1","var2" and so on for the other 23 variables)) Is it right that I define the variables as ordered (the output returns thresholds suggesting I should). Does the cfa command calculate tetrachoric correlations in the background? However, output for the command returns two variables with small negative variances (-0.002) which I think is due to the correlation matrix not being positive definite. Is it reasonable to force these to be zero when defining the model or is this more a sign of pro...

...est() for calculating the correlation coefficient and p values for some data. however, since the data consist of two dichotomous sequences (actually just binary data), i understand that simply using the pearson correlation is not sufficient. however, having done a bit of research i found that the tetrachoric correlation is what i am after. found the polycor package and the polychor routine, which seem to do precisely what i want. however, i don't get p values out of polychor, just the standard deviation. so, in a rather naive way i have tried to write a function which will return a list with simil...

Good Morning, Is it possible to use the R program for a CFA with dichotomous data? Thank you, Kathleen Kathleen Kemp, M.A. Doctoral Clinical Psychology Student, Concentration: Forensic Psychology Drexel University Philadelphia, PA 19104 kk354@drexel.edu [[alternative HTML version deleted]]

...gram always returns a phi-coefficient correlation lower than the continuous correlation. Mathematically, I guess this is expected because the phi-coefficient is partially a function of the percentage of positive responses. This, in turn, explains Pearson's (1900) interest in the whole area of tetrachoric correlations -- a tetrachoric correlation being the Pearson product moment correlation that would have been observed had two dichotomously scored variables been measured on a continuous scale (Pearson, 1900). Appreciate any additional input or possible solutions. Paul -----Original Message----...

I am trying to cluster some binary data using k-means . As the regular "kmeans" available from stats package in R does'nt provide the option to change the distance method. I was wondering there is any package available to specify type of distance measure to be used in k means clustering in R. Especially distances like "Jaccard" which is good for binary data.

Hi I am looking for a structural equation modeling package in R which can be used for categorical data. Is anyone aware of the existence of such a package? Would appreciate any help on this. Thank you Upasna -- --------------------------------------------------------------------- Upasna Sharma Research Scholar Shailesh J. Mehta School of Management, Indian Institute of Technology, Bombay

Dear R-users Could anyone tell me which library contains a function to compute polycoric correlations? I wonder the same question was asked a while ago, but I could not locate the mail in the R-help archives. Sorry for bothering you. Sincerely ------------------------ Hiroto Miyoshi ???? h_m_ at po.harenet.ne.jp

Hello, I'd like to know if there is a way to fit a Structural equation model with dichotomous indicators (ex: problem with a phone solved/ or not) having effects on a ordinal variable. How I do that using R? Do you have an example with the code in R that you can send to me? Thanks a lot! Renata Estrella UFRJ, Brasil, Rio de Janeiro Renata Leite Estrella Assistente de

Hi, we are trying to do structural equation modelling on R. However, one of our predictor variables is categorical (smoker/nonsmoker). Now, if we want to run the sem() command (from the sem library), we need to specify a covariance matrix (cov). However, Pearson's correlation does not work on the dichotomous variable, so instead we produced a covariance matrix using the Spearman's (or

I am looking to fit one or more latent categorical variables to data that is a mixture of categorical and continuous variables. Factor analysis would work for continuous data, latent class analysis for categorical data. I understand that in a package such as MPlus I could perform a single analysis of both data types. Are there similar routines available in R? Stuart -----Original Message-----

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

...t at JohnDesktop8300> Content-Type: text/plain; charset="us-ascii" Dear Upasna, I apologize for responding so late, but I was out of town when you posted your query to r-help. The sem() function in the sem package can handle dichotomous and ordered categorical observed variables via tetrachoric, polychoric, biserial, and polyserial correlations computed by the polycor package. See in particular the hetcor() function in that package, which can compute "heterogeneous" correlation matrices. Standard errors for parameter estimates in the SEM can then be computed by bootstrapping; se...