tcc {birtr}

Test Characteristic Curve

Description

Plots a test characteristic curve from a set of item parameters under the one-, two-, or three-parameter logistic model.

Usage

tcc(b, a, c)

Arguments

b

a numeric vector representing the values of item difficulty.

a

a numeric vector representing the values of item discrimination.

c

a numeric vector representing the values 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. The length of b should be the same as that of a and c. Each 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 each c. Under the one-parameter logistic model, a = rep(1, length(b)) and c = rep(0, length(b)). Under the two-parameter logistic model, c = rep(0, length(b)).

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

b <- c(-2.0, -1.0, 0.0, 1.0, 2.0)
a <- c(0.5, 0.75, 1.0, 0.75, 0.5)
c <- c(.2, .2, .2, .2, .2)
tcc(b, a, c)
tcc(a = a, b = b, c = c)
tcc(b)    # tcc(b, a = rep(1, length(b)), c = rep(0, length(b)))
tcc(b, a) # tcc(b, a, c = rep(0, length(b)))