ltm, and a
variety of functions useful with IRT models. The irtoys package contains a bunch of functions
potentially useful to those teaching or learning Item
Response Theory (IRT). Although there is no shortage of
good IRT programs, those tend to have wildly different
and often unwieldy user interfaces. Besides, no single
program does everything one needs. Item parameters can be
estimated with a program like ICL or BILOG,
non-parametric approaches are implemented in TestGraf,
transformation to a common scale needs ST, and so on.
Some programs, such as ICL, have no graphical
capabilities at all, while others offer stunning
interactive graphics but refuse to output a Postscript
file.
Package irtoys provides a common interface to some
of the most basic functions in ICL, BILOG, and 's own
ltm, some of the functionality of TestGraf and ST,
and a variety of other functions. Those who want to take
advantage of the full functionality of ICL, BILOG & Co.
must still master their syntax.
To take full advantage of irtoys, some IRT
software is needed. Package ltm is automatically
loaded. ICL by Brad Hanson can be downloaded from his
site,
On Windows, make sure that the executable files
(icl.exe for ICL, BLM1.EXE,
BLM2.EXE, and BLM3.EXE for BILOG) are
located in a directory that is included in the PATH
variable. On Linux, BILOG, being a Windows program, is
run with wine, and should also be on a path where
wine can find it. On my machine, I have simply put the
three files in ~/.wine/drive_c/windows/. It seems
that new versions of wine expect them to be explicitly
tagged as executable. On Macintosh, at least ltm
should work in all cases.