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oneil
2011 Nov 11
2
Estimating IRT models by using nlme() function
...persons as random effects, and item parameters as fixed
effects. To fit Rasch model, I run the following code:
d <- read.table("data.txt", header=TRUE)
d1 <- d$d1
d2 <- d$d2
d3 <- d$d3
d4 <- d$d4
d5 <- d$d5
###########################################################
onePL <- function(b1,b2,b3,b4,b5,theta) { #nonlinear model to fit
b= b1*d1+b2*d2+b3*d3+b4*d4+b5*d5
exp((theta-b))/(1+exp((theta-b)))
}
#####################################################################
nlme(model=Response ~ onePL(b1,b2,b3,b4,b5,theta),
data = d,
fixed = b1+b2+b3+b4+b5 ~ 1,...