icc {birtr} | R Documentation |

## Item Characteristic Curve

### Description

Plots an item characteristic curve under the one-, two-, or three-parameter logistic model.

### Usage

```
icc(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`

.
The vertical dotted line corresponds to the value of the item difficulty
parameter.

### 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

```
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)
```

*birtr*version 1.0.0 Index]