iccfit {birtr} | R Documentation |

## Item Characteristic Curve Fitting

### Description

Plots the item characteristic curve and the simulated observed proportions of correct response from the one-, two-, or three-parameter logistic model.

### Usage

```
iccfit(mdl)
```

### Arguments

`mdl` |
1, 2, or 3 representing the number of the model parameters. |

### 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.
With the number of item characteristic curve model parameters `mdl`

the item parameters are randomly sampled from the uniform distributions; for
example, under the three-parameter logistic model, `b`

from the -3 to
3 range, `a`

from the 0.2 to 2.8 range, and `c`

from the 0 to
.35 range.
Each of the 33 ability levels from the -3 to +3 range with .1875 interval,
the observed proportion of correct response is generated from the binomial
distribution for sample size of 21.
The chi-square goodness-of-fit index is obtained and reported with the
set of item parameters.

### 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

```
iccfit(1)
iccfit(2)
iccfit(3)
```

*birtr*version 1.0.0 Index]