tcc {birtr}R Documentation

Test Characteristic Curve


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


tcc(b, a, c)



a numeric vector representing the values of item difficulty.


a numeric vector representing the values of item discrimination.


a numeric vector representing the values 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. 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)).


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


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)))

[Package birtr version 1.0.0 Index]