tif {birtr} R Documentation

## Test Information Function

### Description

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

### Usage

tif(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)). In case b to be a single number, then the plot contains the item informaiton function. Note that the maximum of the information value on the vertical axis of the graph is arbitrarily set to 10.

### 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(-1.0, -0.5, 0.0, 0.5, 1.0)
a <- c(2.0, 1.5, 1.5, 1.5, 2.0)
c <- c(.2, .2, .2, .2, .2)
tif(b, a, c)
tif(a = a, b = b, c = c)
tif(b)    # tif(b, a = rep(1, length(b)), c = rep(0, length(b)))
tif(b, a) # tif(b, a, c = rep(0, length(b)))


[Package birtr version 1.0.0 Index]