[R] Simulating dataset using Parallel Latent CTT model?

[William Revelle]

Nidhi,

As I said in my previous response, if you want 20 items with equal 
factor loadings you can just specify the loading: e.g., for all 
loadings of .6
GenData <- congeneric.sim(N=500, loads = rep(.6,20), short = FALSE)

The error variances will all be equal to 1 - loading^2  where loading 
is the factor loading you specified.

This is R.  If you want to know how a function works,  list the source code.

Bill





At 9:47 AM -0500 12/27/08, Nidhi Kohli wrote:
>Hi Bill,
>
>Thank you very much for your response. You are right, I want to 
>simulate data set for 500 examinees across 20 items using Parallel 
>latent CTT model. As you know in Parallel Latent CTT model all the 
>error variances and factor loadings are equal across all the items. 
>Could you please let me know how can I incorporate common error 
>variance for 20 items in this R-program?
>
>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
>***************************************
>
>
>---- Original message ----
>  >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
>>>
>>>______________________________________________
>>>R-help at 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.
>>
>>
>>--
>>William Revelle		http://personality-project.org/revelle.html
>>Professor			http://personality-project.org/personality.html
>>Department of Psychology             http://www.wcas.northwestern.edu/psych/
>>Northwestern University	http://www.northwestern.edu/
>>Attend  ISSID/ARP:2009               http://issid.org/issid.2009/


-- 
William Revelle		http://personality-project.org/revelle.html
Professor			http://personality-project.org/personality.html
Department of Psychology             http://www.wcas.northwestern.edu/psych/
Northwestern University	http://www.northwestern.edu/
Attend  ISSID/ARP:2009               http://issid.org/issid.2009/