item_info {eRm} R Documentation

Calculate Item Information for 'eRm' objects

Description

Calculates Samejima's (1969) information for all items

Usage

item_info(ermobject, theta = seq(-5, 5, 0.01))

i_info(hvec, itembeta, theta)


Arguments

 ermobject An object of class 'eRm'. theta Supporting or sampling points on the latent trait. hvec Number of categories of a single item. itembeta Cumulative item category parameters for a single item.

Details

The function item_info calculates information of the whole set of items in the 'eRm' object. The function i_info does the same for a single item (and is called by item_info).

Value

Returns a list (i_info) or a list of lists (where each element corresponds to an item, item_info) and contains

 c.info Matrix of category information in columns for the different theta values in rows. i.info Vector of item information for the different theta values.

Thomas Rusch

References

Samejima, F. (1969) Estimation of latent ability using a response pattern of graded scores. Psychometric Monographs, 17.

The function to calculate the test information, test_info and the plot function plotINFO.
res <- PCM(pcmdat)