combine.pars: Combine Item Parameters for Multiple Groups

Description

This function combines objects of class and/or sep.pars into a single irt.pars object

Usage

combine.pars(x, common, grp.names)

Arguments

an ordered list containing two or more irt.pars objects, two or more sep.pars objects, or a combination of irt.pars and sep.pars objects.

common

an n x 2 matrix or list of matrices identifying the common items between adjacent pairs of objects in x. See below for more details.

grp.names

character vector of names for all the groups in the returned object

Value

Returns an object of class

Details

Although many of the methods in this package allow for lists containing irt.pars and sep.pars objects, it may be helpful to combine the item parameters for multiple groups into a single object. x can include a combination of irt.pars and sep.pars objects. The irt.pars objects can contain information for a single group or multiple groups. The list elements in x should be ordered such that adjacent elements correspond to adjacent groups. If an irt.pars object is included with multiple groups, the list element following this object should contain information for a group that is adjacent to the last group in the irt.pars object. If x contains only two elements, common should be a matrix. If x contains more than two elements, common should be a list. In any of the common matrices the first column identifies the common items for the first group of two adjacent list elements in x. The second column in common identifies the corresponding set of common items from the next list element in x. For example, if x contains only two list elements, a single set of common items links them together. If item 4 in group one (row 4 in slot pars) is the same as item 6 in group two, the first row of common would be "4,6". If an irt.pars object is included with multiple groups, common should correspond to the set of common items between the last group in the irt.pars object and the group in the adjacent element in x.

References

Weeks, J. P. (2010) plink: An R package for linking mixed-format tests using IRT-based methods. Journal of Statistical Software, 35(12), 1--33. URL http://www.jstatsoft.org/v35/i12/