Problem with using simdata with graded response model

[Varun Aggarwal]

hi 

Hi guys, 

I am trying to use simdata to simulate graded response model. Here's what I am trying to do.  

a<-1

d<-c(1,0,-1)

dat1<-simdata(a=1,d=d,N=10). However, when I run this snippet of code I get a result where all the values in dat1 are 4.

 

The parameters as defined in the above code work and I verified that using itemplot(shiny=T). 

I am not sure what is it that I am doing wrong. Any help would be appreciated. 

Thanks,
 Varun

[Phil Chalmers]

The d input here should be a matrix, not a vector, where each row corresponds to a single item. It might be helpful just to follow the examples in simdata() and modify those until it suits your need.

Phil

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[Alexis Georgeson]

Hi, 

I am having the same issue generating data from the graded model where all item responses are 4s. Input for d is a matrix.  I have the most recent version of mirt and have looked at the examples in simdata() and can't figure out what is happening.  Here is a reproducible example: 

 a <- matrix(rlnorm(3,.2,.3))

 b <- matrix(c(0.325,1.430,2.485,

-0.885,0.265, 0.980,

-0.630,0.270,1.320),byrow=TRUE,nrow=3)

 dat <- simdata(a=a, d=b, 1000, itemtype = 'graded')

thanks,

Alexis 

On Wednesday, January 22, 2020 at 10:19:34 PM UTC-5, Phil Chalmers wrote:

The d input here should be a matrix, not a vector, where each row corresponds to a single item. It might be helpful just to follow the examples in simdata() and modify those until it suits your need.

Phil

On Thu, Jan 16, 2020 at 4:52 PM Varun Aggarwal <varunagg...@gmail.com> wrote:

hi 

Hi guys, 

I am trying to use simdata to simulate graded response model. Here's what I am trying to do.  

a<-1

d<-c(1,0,-1)

dat1<-simdata(a=1,d=d,N=10). However, when I run this snippet of code I get a result where all the values in dat1 are 4.

 

The parameters as defined in the above code work and I verified that using itemplot(shiny=T). 

I am not sure what is it that I am doing wrong. Any help would be appreciated. 

Thanks,
 Varun

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[Phil Chalmers]

See the traditional2mirt() function. It looks like you are using the classical difficultly-discrimination parameterization rather than the required slope-intercept form.  

Phil

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