transpar: Transform the IRT Parameters

In cswells1/MeasInv: Collection of Methods to Detect Dichotomous and Polytomous Differential Item Functioning (DIF)

Description

This function transforms item parameters using estimated IRT linking coefficients.

Usage

transpar(x, constants)

Arguments

x	A data.frame containing the item meta data (e.g., item parameters, number of categories, models ...). This data.frame can be easily obtained using the function shape_df. See preplink, test.info, or simdat for more details about the item meta data.
constants	A vector of length two containing the IRT linking coefficients (i.e., slope and intercept). The first value is a slope and the second value is an intercept.

Value

This function returns a data.frame containing the transformed item parameters.

Author(s)

Hwanggyu Lim [e-mail]

Examples

## IRT liking using single-format tests
# use "KBneat" data set
dat_base <- KBneat$item$dat.base
dat_new <- KBneat$item$dat.new

# specify common items
common.b <- KBneat$common$common.b
common.n <- KBneat$common$common.b

# prepare a data set for IRT linking
x <- preplink(dat_base, dat_new, common.b, common.n)

# estimate IRT linking coefficients using the Mean/Sigma method
rst <- irtlink(x, method.link = 'SL', D = 1.7)

# extract the estimated linking coefficients
constants <- takelink(rst, "coefficients")

# transform the item parameters in the new test form
transpar(dat_new, constants)

cswells1/MeasInv documentation built on Dec. 19, 2021, 7 p.m.