Item Characteristic Curve
Plots an item characteristic curve under the one-, two-, or three-parameter logistic model.
icc(b, a, c)
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. |
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.
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
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)
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