Computes the deviance, which is useful for model comparison.
# S3 method for class 'fisher_mle'
deviance(object, null_model = NULL, ...)Deviance value
When called with a single model, returns -2 * logL (the deviance relative to a saturated model).
When called with two models, returns the deviance difference: D = 2 * (logL_full - logL_reduced)
Under the null hypothesis that the reduced model is correct, D is asymptotically chi-squared with df = p_full - p_reduced.