geostan (version 0.8.1)

waic: Model comparison

Description

Deviance Information Criteria (DIC) and Widely Application Information Criteria (WAIC) for model comparison.

Usage

waic(object, pointwise = FALSE, digits = 2)
dic(object, digits = 1)

Value

WAIC returns a vector of length 3 with the WAIC value, a penalty term which measures the effective number of parameters estimated by the model Eff_pars, and log predictive density Lpd. If pointwise = TRUE, results are returned in a data.frame.

DIC returns a vector of length 2: the DIC value and the penalty term (which is part of the DIC calculation).

Arguments

object

A fitted geostan model

pointwise

Logical (defaults to FALSE), should a vector of values for each observation be returned?

digits

Round results to this many digits.

Details

WAIC (widely applicable information criteria) and DIC (deviance information criteria) are used for model comparison. They are based on theories of out-of-sample predictive accuracy. The DIC is implemented with penalty term defined as 1/2 times the posterior variance of the deviance (Spiegelhatler et al. 2014).

The limitations of these methods include that DIC is less robust than WAIC and that WAIC is not strictly valid for autocorrelated data (viz. geostan's spatial models).

For both DIC and WAIC, lower values indicate better models.

Examples

data(georgia)

fit <- stan_glm(log(rate.male) ~ 1, data = georgia,
                iter=600, chains = 2, quiet = TRUE)
fit2 <- stan_glm(log(rate.male) ~ log(income), data = georgia,
                centerx = TRUE, iter=600, chains = 2, quiet = TRUE)

dic(fit)
dic(fit2)

waic(fit)
waic(fit2)