mirt: Target argument

[Laurien Adriaenssens]

Hello Phil

I'm having difficulties using the Target = .. argument in the mirt function. I already tried a couple of things but get the same error report every time:

Error in validObject(.Object) : 

  invalid class “SingleGroupClass” object: invalid object for slot "Target" in class "SingleGroupClass": got class "matrix", should be or extend class "numeric"

Could you please take a look at my syntax and let me know where I've made an error? Thanks!

data <- expand.table(LSAT7)

a <- matrix(c(1,0,

              1,0,

              1,0,

              0,1,

              0,1), ncol=2, byrow=FALSE)

(mod1 <- mirt(data, 2, Target=a, rotate="targetQ"))

[Phil Chalmers]

Hi Laurien,

I'm afraid you've discovered some older code inputs for mirt(), which I'll be sure to remove in future versions to avoid confusion. By default the 'oblimin' rotation is used exclusively, and all other rotation arguments are passed to summary() instead. So to use the targetQ rotation, do the following:

data <- expand.table(LSAT7)

a <- matrix(c(1,0,

              1,0,

              1,0,

              0,1,

              0,1), ncol=2, byrow=FALSE)

(mod1 <- mirt(data, 2))

summary(mod1, rotate = 'targetQ', Target = a)

Cheers.

Phil

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[Phil Chalmers]

Touched up in the dev version, and listed the change in the NEWS file. https://github.com/philchalmers/mirt/blob/master/NEWS.md. Feel free to install from Github to get the latest version. Cheers.

Phil