Approximate Leave-One-Out (LOO) Cross-validation

Estimates the leave-one-out (LOO) information criterion for dynamite models using Pareto smoothed importance sampling with the loo package.

Usage

# S3 method for class 'dynamitefit'
loo(x, separate_channels = FALSE, thin = 1L, ...)

Arguments

x

[dynamitefit]
The model fit object.

separate_channels

[logical(1)]
If TRUE, computes LOO separately for each channel. This can be useful in diagnosing where the model fails. Default is FALSE, in which case the likelihoods of different channels are combined, i.e., all channels of are left out.

thin

[integer(1)]
Use only every thin posterior sample when computing LOO. This can be beneficial with when the model object contains large number of samples. Default is 1 meaning that all samples are used.

...

Ignored.

Value

An output from loo::loo() or a list of such outputs (if separate_channels was TRUE).

References

Aki Vehtari, Andrew, Gelman, and Johah Gabry (2017). Practical Bayesian model evaluation using leave-one-out cross-validation and WAIC. Statistics and Computing. 27(5), 1413–1432.

See also

Model diagnostics hmc_diagnostics(), lfo(), mcmc_diagnostics()

Examples

data.table::setDTthreads(1) # For CRAN
# \donttest{
# Please update your rstan and StanHeaders installation before running
# on Windows
if (!identical(.Platform$OS.type, "windows")) {
  # this gives warnings due to the small number of iterations
  suppressWarnings(loo(gaussian_example_fit))
  suppressWarnings(loo(gaussian_example_fit, separate_channels = TRUE))
}
#> $y_loglik
#> 
#> Computed from 200 by 1450 log-likelihood matrix.
#> 
#>          Estimate   SE
#> elpd_loo    241.1 27.0
#> p_loo        91.2  3.4
#> looic      -482.2 53.9
#> ------
#> MCSE of elpd_loo is NA.
#> MCSE and ESS estimates assume MCMC draws (r_eff in [0.2, 1.9]).
#> 
#> Pareto k diagnostic values:
#>                           Count Pct.    Min. ESS
#> (-Inf, 0.57]   (good)     1435  99.0%   35      
#>    (0.57, 1]   (bad)        15   1.0%   <NA>    
#>     (1, Inf)   (very bad)    0   0.0%   <NA>    
#> See help('pareto-k-diagnostic') for details.
#> 
# }