Description Details Author(s) References
Package: | irtoys |
Type: | Package |
Version: | 0.1.4 |
Date: | 2011-06-22 |
License: | GPL (>= 2) |
LazyLoad: | yes |
LazyData: | yes |
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.
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, 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.
NOTE: Starting with version 0.1.6, function est
returns a list of two matrices: est
contains the
parameter estimates and is thus identical to the output
in earlier versions, and se
contains the standard
errors, in a similar format. 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(θ_i-b_j) rather than
1.7a^*_j(θ_i-b_j), function est
now
estimates item parameters only in the logistic metric.
Ivailo Partchev <partchev@gmail.com>
S. E. Embretson and S. P. Reise (2000), Item Response Theory for Psychologists, Lawrence Erlbaum Associates, Mahwah, NJ
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