## Efficient simulation-based calibration for Bayesian models

SBC provides tools to easily validate and offer corrections on prior, likelihood, and computation algorithms based on the self-recovering property of Bayesian models. This package contains tools such as SBC rank histograms, ECDF plots, and their summary statistics which can be used to assess computational faithfulness.

### Varieties of calibrations: scope of this package

Calibration (i.e. reliability) is not a sufficient condition for a good forecast but a minimal property that any forecast should satisfy (FV1998). It serves as a bootstrap for model development and its method and target varies. Target is chosen as modeler’s quantity of interest and directly affects the calibrated result as reward in reinforcement learning. Method depends on how much you marginalized or conditioned the full joint space to test coverage. Scope of this package is checked below.

## Interface and Usage

SBC is designed to be primarily used with Stan models, offering a highly customizable interface to integrate Simulation Based Calibration into existing Bayesian workflows with minimal effort. Its main feature is the api interface, which defines a fully-blown SBC pipeline starting from dataset generation to posterior sampling. Once a user has a valid Stan model and a minor R function defining the data generating process(referred to as Generator), running SBC becomes as simple as:

n_datasets <- 100  # Number of SBC iterations to run

sbc_generator <- SBC::function_SBC_generator(Generator)
sbc_dataset <- SBC::generate_datasets(
sbc_generator,
n_datasets)

cmdstan_backend <- SBC::cmdstan_sample_SBC_backend(
cmdstan_model, iter_warmup = 1000, iter_sampling = 1000)

results <- SBC::compute_results(sbc_dataset, cmdstan_backend)
plot_rank_hist(results)

For detailed usage, please refer to the included vignettes.

### Compatibility

Currently SBC supports cmdstan, rstan, and brms models out of the box. However, adding Backends for other platforms is supported.

## Installation

To install the development version of SBC, run

devtools::install_github("hyunjimoon/SBC")

### References:

Theoretical support

Application support

Vignette

• ECDF with codes (new implementation by Teemu Säilynoja will be available in bayesplot and SBC package soon)

## FAQ

How does calibration relate to prediction accuracy?

Comparing the ground truth and the simulated result is a backbone of calibration and comparison target greatly affects the calibrated (i.e. trained) result, similar to reward in reinforcement learning. In this sense, if the U(a(y), theta) term is designed for prediction, the model will be calibrated to have best predictive result as possible.