PPP {edina} R Documentation

## Posterior Predictive Probabilities (PPPs)

### Description

Computes posterior predictive probabilities (PPPs) based on the odds ratios for each pair of items.

### Usage

PPP(object, ...)

## S3 method for class 'edina'
PPP(object, alpha = 0.05, ...)


### Arguments

 object An edina object ... Not used. alpha Defining region to indicate the level of extremeness the data must before the model is problematic.

### Details

PPPs that smaller than 0.05 or greater than 0.95 tend to be extreme and evidence of misfit. As a result, this is more of a heuristic metric.

### Value

The PPP value given the specified alpha value.

### PPP Computation Procedure

1. simulate observed responses \mathbf Y^{(r)} using model parameters from iteration r of the MCMC sampler

2. computing the odds ratio for each pair of items at iteration r as

OR^{(r)} = n_{11}^{(r)}n_{00}^{(r)}/≤ft(n_{10}^{(r)}n_{01}^{(r)}\right)

, where n_{11}^{(r)} is the frequency of ones on both variables at iteration r, n_{10}^{(r)} is the frequency of ones on the first item and zeros on the second at iteration r, etc.; and

3. computing PPPs for each item pair as the proportion of generated OR^{(r)}'s that exceeded elements of the observed odds ratios.

[Package edina version 0.1.1 Index]