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
NEW FEATURES
o new function, tet(), to calculate, quickly, an approximate matrix of
tetrachoric correlations.
BUG FIXES
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.