irtoys-package: Estimate and plot IRT models bor binary responses
Description
Provides a common interface to the estimation of item parameters in IRT models for binary responses with three different programs (ICL, BILOG, and ltm, and a variety of functions useful with IRT models.Details
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
R'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, www.b-a-h.com:
executables are provided for Windows, Linux, and Macintosh. BILOG
is commercial software sold by SSI --- see www.ssicentral.com
for further detail.
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.References
S. E. Embretson and S. P. Reise (2000),
Item Response Theory for Psychologists,
Lawrence Erlbaum Associates,
Mahwah, NJ