Class ""

Description Details Objects from the Class Slots Extends Author(s) See Also


The formal S4 class for This class contains the item parameters and characteristics of the item parameters for one or more groups. When parameters are included for two or more groups, the common items between the different groups are also included.


Objects of class contain all the information necessary to produce expected response probabilities, linking constants (when data for two or more groups are included), and to plot item response curves/surfaces, vector plots, and parameter comparison plots.

Objects from the Class

Objects can be created by calls of the form new("", ...), but this is not encouraged. Use the function instead.



matrix of item parameters for a single group or a list of matrices containing item parameters for two or more groups


vector with length equal to the number of items, identifying the number of response categories for each item for a single group or a list of response category vectors for two or more groups


a poly.mod object for one group or a list of poly.mod objects identifying the items associated with each IRT model (see class poly.mod for more information)


a j x 2 matrix for j common items or a list of matrices identifying the common items between pairs of item parameters


logical vector identifying whether a given set of item parameters (i.e., for a given group) includes a location parameter


the number of groups (i.e. sets of item parameters)


numeric vector identifying the number of modeled dimensions


Class poly.mod, directly. Class list.poly, by class poly.mod, distance 2.


Jonathan P. Weeks

See Also, as.poly.mod

plink documentation built on May 1, 2019, 8:07 p.m.