Item Characteristic Function in mirt package

[Sukanya Moudgalya]

Please see this slideshow, page 42: http://jonathantemplin.com/files/irt/irt07abim/irt07abim_lecture03.pdf

They have calculated overall 'item characteristic function' for polytomous data as shown below: 

I am not sure which function was used to do this calculation. Is there a pre-existing function or was this coded independently? I am very new to this topic and will appreciate any help regarding this matter.  Thanks!! 

[Phil Chalmers]

It looks like the expected score function, though there is no metric for ICF (it should go from something like 0-3 on the y axis). Compare the following code:

library(mirt)

mod <- mirt(Science, 1)

itemplot(mod, 1)

itemplot(mod, 1, type = 'score')

Phil

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[Sukanya Moudgalya]

Thanks so much!

Phil

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[S.A. Mousavi]

Just came across this by chance! 

The only difference between 

itemplot(mod, 1, type = 'score')

and the above-mentioned graph is that in that graph the values of ICF were divided by the value of highest category so it fits the characteristic curve graph (i.e. limiting ICF values between 0 and 1).

HTH,

Amin.

Phil

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