trf function

Test response function

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 $\theta$.

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.

Returns

A list of: - x: A copy of the argument x - f: A vector containing the TRF values

Details

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

Examples

plot(trf(Scored2pl))

See Also

plot.trf, irf

Author(s)

Ivailo Partchev