| Package: | irtoys |
| Type: | Package |
| Version: | 0.2.0 |
| Date: | 2016-01-30 |
| License: | GPL (>= 2) |
| LazyLoad: | yes |
| LazyData: | yes |
The irtoys package contains a bunch of functions potentially useful
to those teaching or learning Item Response Theory (IRT). R being
particularly good at graphics, there is a rich array of plotting
functions to visualize IRT models or assess their fit. Ability estimates
can be estimated by MLE, BME, EAP, WLE. Various IRT scaling methods are supported:
MM, MS, Stocking-Lord, and Hebaera. Last not least, irtoys may be
the only package to estimate Haberman's interaction model, although a new and
more powerful package is in the making.
Currently, there are several R packages that can estimate the item parameters
in various uni- and multidimensional IRT models, but only several years ago one
had to use stand-alone programs that had wildly different and
often unwieldy user interfaces. Besides, no single program does everything
one needs. One of the original purposes of irtoys was to provide a
simple and unified interface to some of the most basic
functions in ICL, BILOG, and R's own ltm, such that beginners could
concentrate on learning IRT rather than syntaxes. Once that these steps
have been made, those wishing to take
advantage of the full functionality of ICL, BILOG & Co. must still master
the syntax of their program of choice.
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, http://www.openirt.com/b-a-h/software/.
Executables and a very detailed manual (not needed to use ICL with
irtoys are provided for Windows, Linux, and Macintosh. The Mac
version probably does not work with the current OS versions but I still
use the Windows and Linux versions without any problem.
BILOG is commercial software sold by SSI --- see https://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.
NOTE: Starting with version 0.2.0, function est returns a list of three
elements: est contains the parameter estimates and is thus identical
to the output in earlier versions, se contains the standard errors,
in a similar format, and vcm contains the variance-covariance matrices
(NULL when using ICL). When passing item parameters to another function that
only needs the estimates, irf(ip) and
irf(ip$est) can be used interchangeably. This facilitates using simulated
item parameters. A function that does require the complete object is .
Also, function itf now returns item fit statistics
as a vector rather than a list. Finally, since most of the functions in irtoys
have been written with the "logistic" metric in mind (i.e., \(a_j(\theta_i-b_j)\)
rather than \(1.7a^*_j(\theta_i-b_j)\), function est now estimates item
parameters only in the logistic metric.
S. E. Embretson and S. P. Reise (2000), Item Response Theory for Psychologists, Lawrence Erlbaum Associates, Mahwah, NJ