BVARResult.marginal_likelihood#

BVARResult.marginal_likelihood()[source]#

The closed-form log marginal likelihood as a comparable record.

Wraps log_marginal_likelihood in a MarginalLikelihoodSelection so it can sit in one compare() table beside simulated estimates – Chib, modified harmonic mean, bridge sampling – from the Gibbs and particle-chain members of the family. The record carries the value with mcse=0.0 and method="analytic", because the number is exact: it uses no draws (n_draws=0) and has no Monte Carlo error. Its source is "BVAR({order}), {prior_label}", so two fits of the same order under different priors remain distinguishable in a table, and its nobs is nobs, which compare() checks across records: a fit of a different order scores a different number of observations and is not comparable on this number without adjustment.

Differences of the log value across records fitted to the same sample are log Bayes factors; compare() converts them to posterior model probabilities under the prior model probabilities it is given.

Return type:

_MarginalLikelihoodSelection

Returns:

The record – log_value, mcse, method, n_draws, source, and nobs.

Example

>>> import numpy as np
>>> from cultivars.multivariate.large_dim.bayesian import BVAR
>>> from cultivars.bayes.evidence import compare
>>> from cultivars.bayes.priors import NormalInverseWishartPrior
>>> rng = np.random.default_rng(0)
>>> y = np.zeros((120, 2))
>>> for t in range(1, 120):
...     y[t] = 0.7 * y[t - 1] + rng.standard_normal(2)
>>> res = BVAR(y, order=1).fit(n_draws=200, seed=0)
>>> record = res.marginal_likelihood()
>>> record.method, record.mcse, record.n_draws
('analytic', 0.0, 0)
>>> record.log_value == res.log_marginal_likelihood
True
>>> record.source
'BVAR(1), niw(l1=0.2, l3=1, l4=100)'

Rank two priors on the same sample:

>>> alt = BVAR(y, order=1, prior=NormalInverseWishartPrior(tightness=0.02))
>>> table = compare(record, alt.fit(n_draws=200, seed=0).marginal_likelihood())
>>> table.rows[0][0]
'BVAR(1), niw(l1=0.2, l3=1, l4=100)'

See also

  • compare() – the table, with Kass and Raftery’s reading of the Bayes factors.

  • HierarchicalBVAR – maximizes this number over the prior’s hyperparameters rather than comparing a hand-picked few.

  • marginal_likelihood(), bridge_sampling(), modified_harmonic_mean() – simulated estimates for results without a closed form.

References

Kass, R. E., & Raftery, A. E. (1995). Bayes factors. Journal of the American Statistical Association, 90(430), 773-795.

Giannone, D., Lenza, M., & Primiceri, G. E. (2015). Prior selection for vector autoregressions. Review of Economics and Statistics, 97(2), 436-451.