trf {irtoys}

Test response function

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 \theta.

Usage

trf(ip, x = NULL)

Arguments

ip

Item parameters: the output of est, or a 3-column matrix corresponding to its first element, est.

x

The values of the latent variable (\theta 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))