A collection of functions useful in learning and practicing IRT, which can be combined into larger programs. Provides basic CTT analysis, a simple common interface to the estimation of item parameters in IRT models for binary responses with three different programs (ICL, BILOG-MG, and ltm), ability estimation (MLE, BME, EAP, WLE, plausible values), item and person fit statistics, scaling methods (MM, MS, Stocking-Lord, and the complete Hebaera method), and a rich array of parametric and non-parametric (kernel) plots. Estimates and plots Haberman's interaction model when all items are dichotomously scored.
New in 0.2.1
Nothing, really, except that I had to provide new links to the ICL files as a result of Dropbox's new policy on shared files. God bless Brad's beautiful soul, 15 years dead and still helping us.
New in 0.2.0
Added functions to estimate and plot the interaction model
Added erf, a function to plot the empirical item response function
Added ssm, a function to produce IRF in the sum score metric
Added ifp, a function to plot IRF with error bounds.
Small improvements in the tia function
Links to download Brad Hanson's ICL program (see the package help page)
CHANGES IN irtoys VERSION 0.1.7
o new function, tet(), to calculate, quickly, an approximate matrix of tetrachoric correlations.
o fixed a bug in function wle() which affected the variance of Warm's weighted estimate of ability in the case of the 3PL model only.