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, www.b-a-h.com: executables are provided for
Windows, Linux, and Macintosh. Because of the technical problems
occasionally encountered with this site, I have set up an alternative
source:
For Linux: https://www.dropbox.com/s/ks72ow7aznmasqd/icl_linux.tar.gz?dl=0
For Windows: https://www.dropbox.com/s/783ka4q3ifkh4ir/icl_win.zip?dl=0
For Macintosh: https://www.dropbox.com/s/z9kji73r59m4pbf/icl_mac.sea.bin?dl=0
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.
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