Change the interval of the outputted abilities in mirt

问题内容:

I’m using mirtand mirtCAT libraries to obtain student’s trait scores with an unidimensional dichotomic 3 parameters logistic model (in witch the items are already callibrated).

How can I change the trait scale interval outputted by fscores? More explicitly, given the vector F1 containing the scores of the N test takers, how to enforce that every entry of F1 is a member of a interval whose extremes are a < b?

I’m using the following code to get the abilities:

library(mirt)
library(mirtCAT)
test <- read.csv(test.csv)
par <- read.csv(par.csv)
a1 <- c(par[,1])
d <- c(par[,2])
g <- c(par[,3])
par <- data.frame(a1,d,g)
mod <- generate.mirt_object(parameters=par,itemtype='3PL')
scores <- fscores(mod,response.pattern=test)

Witch produces abilities from minus infinity to infinity. The documentation does not mention this, but is quite common in IRT analysis for interpretation reasons.

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原文地址:

https://stackoverflow.com/questions/47755982/change-the-interval-of-the-outputted-abilities-in-mirt

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