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###################################################
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# Function: generate_diff_irt
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# Generates item difficulty threshold matrix for
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# IRT model simulation
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###################################################
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generate_diff_irt <- function(J=7,M=4) {
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# if J=7, item 5. Else, item 3
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if(J==7){
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i <- 5
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}
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if(J==4){
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i <- 3
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}
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difficulties = matrix(c(0), J,M-1)
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rownames(difficulties)=paste("item",1:J)
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colnames(difficulties)=paste("Moda", 1:(M-1))
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for (j in 1:J){
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difficulties[j,1] = qnorm(j/(J+1))
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}
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if (M>2) {
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for (j in 1:J){
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for (m in 2:(M-1)){
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difficulties[j,m]= difficulties[j,1]+(m-1)*2/(M-2)
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}
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}
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}
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difficulties = difficulties-mean(difficulties)
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return(difficulties)
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}
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###################################################
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# GENERATE MATRIX FOR SIMULATION
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###################################################
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generate_diff_irt(J=4,M=2)
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generate_diff_irt(J=4,M=4)
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generate_diff_irt(J=7,M=2)
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generate_diff_irt(J=7,M=4)
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