Date: Fri, 26 Dec 2008 11:31:10 -0600
From: William Revelle <lists at revelle.net>
Subject: Re: [R] Simulating dataset using Parallel Latent CTT model?
To: Nidhi Kohli <nidhik at umd.edu>, r-help at r-project.org
Nidhi,
Presumably, you are trying to simulate 20 items all sharing one
general factor but having some error.
The model as you specified it has no error. Thus all the
correlations will be 1 and the factors will not make any sense.
Most items have loadings on a general factor of the order of about
.4 to .6. You might try:
GenData <- congeneric.sim(N=500, loads = rep(.5,20), short = FALSE)
Then you will find that the factor scores found by factor.pa
correlate at .93 with the latent variable.
FactorScore=factor.pa(GenData$observed,1,scores = "TRUE", rotate="none")
round(cor(FactorScore$scores,GenData$latent),2)
Bill
At 8:27 AM -0500 12/26/08, Nidhi Kohli wrote:
I am trying to simulate a dataset using Parallel Latent CTT model
and this is what i have done so far:
(START)
#Importing psych library for all the simulation related functions
library(psych)
# Settting the working directory path to C:/NCME
path="C:/NCME"
setwd(path)
#Using the function to generate the data
GenData <- congeneric.sim(N=500, loads =
c(1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1), short = FALSE)
#Rounding upto 2 decimal places while showing the correlation matrix
round(cor(GenData$observed),2)
#Factor Score
FactorScore=factor.pa(GenData$observed,1,scores = "TRUE", rotate="none")
round(cor(FactorScore$scores,GenData$latent),2)
(END)
Please let me know if I am moving into the right direction, if not
then, please let me know the correct way to simulate the dataset
Thanks in Advance
Regards,
Nidhi Kohli
***************************************
Nidhi Kohli, M.Ed.
Doctoral Student
Department of Measurement, Statistics
and Evaluation
University of Maryland
1230 Benjamin Building
College Park, MD 20742-1115
e-mail: nidhik at umd.edu