M2 after bfactor

[Makrem Ben Youssef]

Hi phil

 

i'm using mirt package and i'm triying to run a bifactor model with two specific factors and one general factor, (number of items =27) the syntax I used is as follows:

mod<- bfactor(datanow, c(1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2))

 

but when I try to get fit statistiics with M2 funnction , i get the error message"

error in solve.default(t(deltac) %*% Xi2 %*% deltac) : 

  system is computationally singular: reciprocal condition number = 7.80612e-18

 

is it possible to use M2 after bfactor just like mirt? or is there something wrong with my syntax?

Please , I have anaother question about model parameters: i'm using a two parameter model and i'm interested in getting the discrimnation and dfifficulties of items, which function can I use to have this other than the summary function which directly displays  the factor scores.

Thanks a lot for your help.

Makrem

[Phil Chalmers]

This is a computational error, implying that a matrix could not be inverted because it is not positive definite. I'm not sure why this occurred, but it always is possible in numerical computations. Could you try installing the dev version and rerunning your model to see if this still occurs. Also, after installing the dev, try passing the option QMC = TRUE to see if that fixes the issue. Cheers.

Phil

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