Differences between EPDIRM and ICL

The computer program IRT Command Language (ICL) supercedes the Estimation Program for Dichotomous IRT Models (EPDIRM). ICL is really a new version of EPDIRM, with the name changed due to the fact that ICL can estimate item parameters for polytomous as well as dichotomous IRT models. Many commands in the last released version of EPDIRM (version 0.011118) remain unchanged in ICL, although there are cases where the name or arguments of a command changed. This page documents command differences in EPDIRM and ICL with the purpose of assisting EPDIRM users in migrating to ICL. The page does not describe every difference in commands between EPDIRM and ICL, but describes the major differences that should allow most EPDIRM command files to be modifed for use with ICL.

Commands with Changed Names

There are several commands whose names changed in ICL, but which function identically in EPDIRM and ICL. The following table gives EPDIRM commands whose name changed and the names of the corresponding command in ICL.

epdirm_start allocate_items_dist
epdirm_end release_items_dist
new_epdirm new_items_dist
num_theta num_latent_dist_points
delete_epdirm delete_items_dist
item_starting_values item_3PL_starting_values
set_default_model set_default_model_dichotomous, set_default_model_polytomous
starting_values starting_values_dichotomous
write_item_param write_item_param_channel
write_latent_dists write_latent_dist_channel

For the write_latent_dists and write_item_param commands some arguments of the commands changed as described in the next section.

Commands with Changed Arguments

There were some cases in which the arguments of a command changed, even though the command name is the same in EPDIRM and ICL. The first argument of the commands item_get_param, item_get_prior_type, and item_get_prior_param identifies the item parameter on which the command operates. In EPDIRM this argument was a character identifying a parameter name. In ICL this argument is a index identifying the position of the parameter in the list of parameters for the item.

Positional arguments in the EPDIRM commands write_item_param (named write_item_param_channel in ICL), write_latent_dist (named write_latent_dists_channel in ICL), read_item_param, and read_latent_dist are optional arguments in ICL.

The positional argument -num_theta and -theta_range of the EPDIRM epdirm_start command have been changed to -num_latent_dist_points and -latent_dist_range, respectively, in the ICL allocate_items_dist command.

New Commands in ICL

The following are some of the commands that were added to ICL.

Bugs in EPDIRM Fixed in ICL

Some bugs in EPDIRM version 0.011118 that are fixed in ICL are:

Software by Brad Hanson

Brad Hanson's Home Page

URL of this page: http://www.b-a-h.com/software/irt/icl/epdirm_differences.html

Last updated: March 1, 2002