catSurv (version 1.3.0)

obsInf: 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

Value

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

See Also

estimateTheta, expectedObsInf

Examples

# NOT RUN {
## 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)

# }