mirt codes

[Afshin]

Dear All,

I'm new to 'mirt'. I'll be thankful if you help with the following:

I am trying to use ‘mirt’ to estimate (confirmatory) between-item multidimensional Rasch model, bifacator Rasch model and higher-order Rasch model.

I toyed around with some of the codes in mirt but what I got are factor loadings and communalities. What apparently I did was factor analysis and not IRT. I know at some deep statistical level factor analysis and IRT are equivalent but as an applied researcher I cannot follow that. What I need is IRT item parameters. I used the following codes:

specific <- c(1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5) 

   

mod1 <- bfactor(data1, specific)

 

mod2 <- mirt(data1, 2)

 

I’ll be very thankful if you provide me with codes to estimate these three models.

Regards

Afshin

[Caroline Lancaster]

Hi Afshin,

To get the item parameters, you would do: coef(mod2).Jason Anastasopoulos. 

[Phil Chalmers]

Hi Afshin,

If you want to fit a bifactor Rasch model you need to constrain the slopes to be equal to each other within each factor. Alternatively, you could just specify each item as type 'Rasch' via the itemtype input argument. Here's an example:

data(SAT12)
data <- key2binary(SAT12,
                   key = c(1,4,5,2,3,1,2,1,3,1,2,4,2,1,5,3,4,4,1,4,3,3,4,1,3,5,1,3,1,5,4,5))
specific <- c(2,3,2,3,3,2,1,2,1,1,1,3,1,3,1,2,1,1,3,3,1,1,3,1,3,3,1,3,2,3,1,2)
mod1 <- bfactor(data, specific, itemtype = 'Rasch')
coef(mod1, simplify=TRUE)

HTH.

Phil

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[Afshin Khosravi]

Thank you Phil.

Is it possible to estimate a second-order Rasch model with 'mirt'?

Is a second-order Rasch model equivalent to a bifactor Rasch model? If the answer is yes is it true for both dichotomous and polytomous items? 

Regards

Afshin

--

Afshin Khosravi, PhD TEFL, MA TEFL, BA Statistics

Routine statistical analyses with SPSS

Item Response Theory (IRT) models: Unidimensional and multidimensioanl dichotomous and polytomous Rasch models; Multifaceted Rasch model; Linear logistic test model; Mixture distribution Rasch model; Cognitive diagnostic models (CDM)

[Phil Chalmers]

Yes, second-order = bifactor model. Hierarchical models are not currently supported by mirt (though see Yung, Thissen, and McLeod (1999). On the relationship between the higher-order factor model and the hierarchical factor model). And yes, the itemtype for dichotomous/polytomous items is not relevant; the relationship is the same.

Phil

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