tauCalculate {Ratings}R Documentation

Posterior Predictive Probabilities from ordrating

Description

Calculates the quantity labeled tau_{pc} in Ho and Quinn (n.d.). tau_{pc} can be thought of as the probability that a randomly chosen rater (from the set of observed raters) will give product p a rating of c given the observed data.

Usage

tauCalculate(out, ndraws = 500)

Arguments

out An output object from the ordrating function.
ndraws The number of Monte Carlo draws used to calculate the posterior predictive probabilities. Must be less than or equal to the number of rows in out.

Details

Section 3.2 of Ho and Quinn (n.d.) provides full details for how tau_{pc} is calculated. The basic ideas are the following.

tauCalculate takes the MCMC output from ordrating and calculates the sample average (over all row units in Y) of the posterior predictive probability of a particular column unit in Y being rated as c. This is done for all column units and ratings categories.

Value

A P x C matrix where P is the number of columns in Y and C is the number of ordinal rating categories. Each row of this matrix gives the posterior predictive probability that a randomly chosen rater, from the set of observed raters, will give product p a rating of c.

References

Ho, Daniel E. and Kevin M. Quinn. forthcoming. "Improving the Presentation and Interpretation of Online Ratings Data with Model-based Figures." The American Statistician.

See Also

ordrating, barplotModelBased, starplotModelBased

Examples

## Not run: 
## Mondo Times example from Ho & Quinn (nd).
## may have to increase stack limit to run this example on some machines

data(Mondo)

ord.out <- ordrating(Mondo, beta.constraint=1, tune=.035, 
                     ma=1, mb=-5, vinva=1, vinvb=0.05,
                     gamma.start=c(-300, 0, 1.5, 3.0, 4.5, 300),
                     thin=20, burnin=20000, mcmc=100000, verbose=1000)

tau <- tauCalculate(ord.out, 500)



## subsetting the Mondo data to include only raters who rated 5 or more 
## outlets (should avoid any stacksize problems)

Mondo.sub <- Mondo[apply(!is.na(Mondo), 1, sum) >= 5, ]
## also getting rid of outlets that are not rated now
Mondo.sub <- Mondo.sub[,apply(is.na(Mondo.sub), 2, mean) != 1] 

ord.out <- ordrating(Mondo.sub, beta.constraint=1, tune=.035, 
                     ma=1, mb=-5, vinva=1, vinvb=0.05,
                     gamma.start=c(-300, 0, 1.5, 3.0, 4.5, 300),
                     thin=20, burnin=20000, mcmc=100000, verbose=1000)

tau <- tauCalculate(ord.out, 500)

## End(Not run)

[Package Ratings version 0.1-1 Index]