trf {irtoys} | R Documentation |
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.
A common use of this function would be to obtain a plot of the TRF.
trf(ip, x = NULL)
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 (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. |
A list of:
x |
A copy of the argument x |
f |
A vector containing the TRF values |
Ivailo Partchev
data(Scored) p.2pl <- est(Scored, model="2PL", engine="ltm") plot(trf(p.2pl))