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https://github.com/stan-dev/loo

loo R package for approximate leave-one-out cross-validation (LOO-CV) and Pareto smoothed importance sampling (PSIS)
https://github.com/stan-dev/loo

bayesian bayesian-data-analysis bayesian-inference bayesian-methods bayesian-statistics cross-validation information-criterion model-comparison r-package stan

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loo R package for approximate leave-one-out cross-validation (LOO-CV) and Pareto smoothed importance sampling (PSIS)

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# loo

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### Efficient approximate leave-one-out cross-validation for fitted Bayesian models

__loo__ is an R package that allows users to compute efficient approximate
leave-one-out cross-validation for fitted Bayesian models, as well as model
weights that can be used to average predictive distributions.
The __loo__ package package implements the fast and stable computations for
approximate LOO-CV and WAIC from

* Vehtari, A., Gelman, A., and Gabry, J. (2017). Practical Bayesian model
evaluation using leave-one-out cross-validation and WAIC.
_Statistics and Computing_. 27(5), 1413--1432.
doi:10.1007/s11222-016-9696-4. [Online](https://link.springer.com/article/10.1007/s11222-016-9696-4),
[arXiv preprint arXiv:1507.04544](https://arxiv.org/abs/1507.04544).

and computes model weights as described in

* Yao, Y., Vehtari, A., Simpson, D., and Gelman, A. (2018). Using
stacking to average Bayesian predictive distributions. In Bayesian
Analysis, doi:10.1214/17-BA1091.
[Online](https://projecteuclid.org/euclid.ba/1516093227),
[arXiv preprint arXiv:1704.02030](https://arxiv.org/abs/1704.02030).

From existing posterior simulation draws, we compute approximate LOO-CV using
Pareto smoothed importance sampling (PSIS), a new procedure for regularizing
importance weights. As a byproduct of our calculations, we also obtain
approximate standard errors for estimated predictive errors and for comparing
predictive errors between two models. We recommend PSIS-LOO-CV instead of WAIC,
because PSIS provides useful diagnostics and effective sample size and Monte
Carlo standard error estimates.

### Resources

* [mc-stan.org/loo](https://mc-stan.org/loo) (online documentation, vignettes)
* [Ask a question](https://discourse.mc-stan.org) (Stan Forums on Discourse)
* [Open an issue](https://github.com/stan-dev/loo/issues) (GitHub issues for bug reports, feature requests)

### Installation

* Install the latest release from CRAN:

```r
install.packages("loo")
```

* Install the latest development version from GitHub:

```r
# install.packages("remotes")
remotes::install_github("stan-dev/loo")
```

We do _not_ recommend setting `build_vignettes=TRUE` when installing from GitHub
because some of the vignettes take a long time to build and are always available
online at [mc-stan.org/loo/articles/](https://mc-stan.org/loo/articles/).

### Python and Matlab/Octave Code

Corresponding Python and Matlab/Octave code can be found at the
[avehtari/PSIS](https://github.com/avehtari/PSIS) repository.

### License

The code is distributed under the GPL 3 license. The documentation is distributed under the CC BY 4.0 license.