icc {birtr}

Item Characteristic Curve

Description

Plots an item characteristic curve under the one-, two-, or three-parameter logistic model.

Usage

icc(b, a, c)

Arguments

b

a single number representing the value of item difficulty.

a

a single number representing the value of item discrimination.

c

a single number representing the value of lower asymptote.

Details

While the theoretical range of ability is from negative infinity to positive infinity, practical considerations usually limit the range of values from -3 to +3. Under the one-parameter logistic model, a = 1 and c = 0. Under the two-parameter logistic model, c = 0. The parameter c has a theoretical range from 0 to 1, but in practice values above .35 are not considered acceptable, hence use the range from 0 to .35 for c. The vertical dotted line corresponds to the value of the item difficulty parameter.

References

Baker, F. B., & Kim, S.-H. (2017). The basics of item response theory using R. New York, NY: Springer. ISBN-13: 978-3-319-54204-1

Examples

icc(1.5, 1.3, .2)
icc(a = 1.3, b = 1.5, c = .2)
icc(1)      # icc(1, 1, 0)
icc(1, 0.5) # icc(1, 0.5, 0)