trf: Test response function

In lebebr01/irtoys-2: Simple interface to the estimation and plotting of IRT models

Description

Returns the test response function (TRF) of the 3PL (1PL, 2PL) model. The TRF is the sum of the item response functions (IRF) in a test, and represents the expected score as a function of the latent variable θ.

Usage

  trf(ip, x = NULL)

Arguments

ip	Item parameters: a matrix with one row per item, and three columns: [,1] item discrimination a, [,2] item difficulty b, and [,3] asymptote c.
x	The values of the latent variable (θ in the equation above), at which the IRF will be evaluated. If not given, 99 values spaced evenly between -4 and +4 will be used, handy for plotting.

Details

A common use of this function would be to obtain a plot of the TRF.

Value

A list of:

x	A copy of the argument x
f	A vector containing the TRF values

Author(s)

Ivailo Partchev

See Also

plot.trf, irf

Examples

plot(trf(Scored2pl$est))

lebebr01/irtoys-2 documentation built on May 20, 2019, 11:29 p.m.