The equateMultiple package computes:
Data preparation follows the same steps of the equateIRT package.
Load the package equateMultiple and the data
library("equateMultiple") data("data2pl", package = "equateIRT")
Estimate a two parameter logistic model for 5 data sets with the R package ltm
library("ltm") m1 <- ltm(data2pl[[1]] ~ z1) m2 <- ltm(data2pl[[2]] ~ z1) m3 <- ltm(data2pl[[3]] ~ z1) m4 <- ltm(data2pl[[4]] ~ z1) m5 <- ltm(data2pl[[5]] ~ z1)
Extract the item parameter estimates and the covariance matrices
estm1 <- import.ltm(m1, display = FALSE) estm2 <- import.ltm(m2, display = FALSE) estm3 <- import.ltm(m3, display = FALSE) estm4 <- import.ltm(m4, display = FALSE) estm5 <- import.ltm(m5, display = FALSE) estm1$coef[1:3, ] estm1$var[1:3, 1:3]
Create a list of coefficients and covariance matrices
estc <- list(estm1$coef, estm2$coef, estm3$coef, estm4$coef, estm5$coef) estv <- list(estm1$var, estm2$var, estm3$var, estm4$var, estm5$var) test <- paste("test", 1:5, sep = "")
Create an object of class modIRT
mods <- modIRT(coef = estc, var = estv, names = test, display = FALSE) coef(mods$test1)[1:5]
The linkage plan
lplan<-linkp(coef = estc) lplan
Estimation of the equating coefficients using the multiple mean-mean method. Form 1 is the base form.
eqMM <- multiec(mods = mods, base = 1, method = "mean-mean") summary(eqMM)
Estimation of the equating coefficients using the multiple mean-geometric mean method.
eqMGM <- multiec(mods = mods, base = 1, method = "mean-gmean") summary(eqMGM)
Estimation of the equating coefficients using the multiple item response function method.
eqIRF<-multiec(mods = mods, base = 1, method = "irf") summary(eqIRF)
Estimation of the equating coefficients using the multiple item response function method. The initial values are the estimates obtained with the multiple mean-geometric mean method.
eqMGM <- multiec(mods = mods, base = 1, method = "mean-gmean", se = FALSE) eqIRF<-multiec(mods = mods, base = 1, method = "irf", start = eqMGM) summary(eqIRF)
Estimation of the equating coefficients using the multiple test response function method.
eqTRF<-multiec(mods = mods, base = 1, method = "trf") summary(eqTRF)
The synthetic item parameters and their standard errors can be extracted as follows (using the multiple item response function method).
eqIRF$as eqIRF$bs eqIRF$se.as eqIRF$se.bs
Equated scores with the true score equating method
scTSE<-score(eqIRF) round(scTSE,3)
Equated scores with the observed score equating method, avoiding computation of standard errors
scOSE<-score(eqIRF, method = "OSE", se = FALSE) round(scOSE,3)
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