Brings up a dialog to specify how many plots should be grouped together on a single line. Initially, plots are stacked one-across. Component Curves shows four plots across.

The ability is computed using the IRT Ability function. The function has the following form

where Q1, Q2,...,Qn are columns from the data table containing items, a1, a2,..., an are the corresponding discrimination parameters, b1, b2,..., bn are the corresponding difficulty parameters for the items, and c1, c2, ..., cn are the corresponding threshold parameters. Note that the parameters are entered as a matrix, enclosed in square brackets.