prior {catSurv} R Documentation

## Evaluate the Prior Density Distribution at Position theta

### Description

Calculates the density at `theta` of either the normal, Student's t, or uniform distribution.

### Usage

```prior(catObj, theta)
```

### Arguments

 `catObj` An object of class `Cat`. `theta` A numeric value at which to evaluate the prior

### Details

The `priorName` slot of `Cat` object needs to be either `"UNIFORM"`, `"NORMAL"`, or `"STUDENT_T"`.

When `priorName` slot is `"NORMAL"`, the first element of `priorParams` slot is the mean, the second element is the standard deviation.

When `priorName` slot is `"STUDENT_T"`, the first element of `priorParams` slot is the non-centrality parameters and the second is degrees of freedom.

When `priorName` slot is `"UNIFORM"`, the elements of the `priorParams` slot are the lower and upper bounds, of the interval, respectively. Note that the `"UNIFORM"` is only applicable for the expected a posteriori (EAP) estimation method.

### Value

The function `prior` returns a numeric consisting of prior value, π(θ), given the value θ.

### 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.

This function uses Boost `C++` source libraries for the uniform and Student's t distributions and calls `dnorm4` written in `C` which is identical to that of `dnorm` in `R`.

### Author(s)

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

`Cat-class`

### Examples

```## Loading ltm Cat object
data(ltm_cat)

## Prior calculation for different distributions
ltm_cat@priorName <- "NORMAL"
ltm_cat@priorParams <- c(0, 1) ## Parameters are mean and standard deviation
prior(ltm_cat, theta = 1)

ltm_cat@priorName <- "STUDENT_T"
ltm_cat@priorParams <- c(1, 3) ## Parameters are non-centrality param and degrees of freedom
prior(ltm_cat, theta = 1)

ltm_cat@priorName <- "UNIFORM"
ltm_cat@priorParams <- c(-1, 1) ## Parameters are lower bound and upper bound of interval
prior(ltm_cat, theta = 1)

```

[Package catSurv version 1.4.0 Index]