icccal {birtr} R Documentation

## Item Characteristic Curve Calculations

### Description

Computes the logistic deviate L, the exponent of negative L, the denominator, and the value of probability of correct response for each of seven ability levels evenly spaced from -3 to +3 under the one-, two-, or three-parameter logistic item characteristic curve model.

### Usage

icccal(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.

### 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

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


[Package birtr version 1.0.0 Index]