obsInf {catSurv} R Documentation

## Observed Information

### Description

Calculates the observed information of the likelihood of a respondent's ability \theta for a given item.

### Usage

obsInf(catObj, theta, item)


### Arguments

 catObj An object of class Cat theta A numeric or an integer indicating the value for \theta item An integer indicating the index of the question item

### Details

The observed information is equivalent to the negative second derivative of the log-likelihood evaluated at \theta. This function should never be called when the respondent has answered no questions as the likelihood is not defined.

### Value

The function obsInf returns a numeric value of the observed information of the likelihood, given \theta, for a given question item.

### Note

This function is to allow users to access the internal functions of the package. During item selection, all calculations are done in compiled C++ code.

### Author(s)

Haley Acevedo, Ryden Butler, Josh W. Cutler, Matt Malis, Jacob M. Montgomery, Tom Wilkinson, Erin Rossiter, Min Hee Seo, Alex Weil

### See Also

estimateTheta, expectedObsInf

### Examples

## Loading ltm Cat object
data(ltm_cat)

## Store example answers
setAnswers(ltm_cat) <- c(1,0,1,0,1, rep(NA, 35))

## Calculate observed information for different ability parameters and items
obsInf(ltm_cat, theta = 1, item = 10)
obsInf(ltm_cat, theta = 1, item = 11)
obsInf(ltm_cat, theta = 0, item = 10)
obsInf(ltm_cat, theta = 0, item = 11)



[Package catSurv version 1.4.0 Index]