Calculate Item Information for 'eRm' objects

Description

Calculates Samejima's (1969) information for all items

Usage

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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.

Author(s)

Thomas Rusch

References

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

See Also

The function to calculate the test information, test_info and the plot function plotINFO.

Examples

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res <- PCM(pcmdat)
info <- item_info(res)
plotINFO(res,type="item")

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