obsInf {catSurv}

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)