statsmodels.tools.eval_measures.aic_sigma¶
-
statsmodels.tools.eval_measures.aic_sigma(sigma2, nobs, df_modelwc, islog=
False)[source]¶ Akaike information criterion.
- Parameters:¶
- sigma2
float estimate of the residual variance or determinant of Sigma_hat in the multivariate case. If islog is true, then it is assumed that sigma is already log-ed, for example logdetSigma.
- nobs
int number of observations
- df_modelwc
int number of parameters including constant
- islogbool
If True, sigma2 is already log-transformed.
- sigma2
- Returns:¶
- aic
float information criterion
- aic
Notes
A constant has been dropped in comparison to the loglikelihood base information criteria. The information criteria should be used to compare only comparable models.
For example, AIC is defined in terms of the loglikelihood as
\(-2 llf + 2 k\)
in terms of \(\hat{\sigma}^2\)
\(log(\hat{\sigma}^2) + 2 k / n\)
in terms of the determinant of \(\hat{\Sigma}\)
\(log(\|\hat{\Sigma}\|) + 2 k / n\)
Note: In our definition we do not divide by n in the log-likelihood version.
TODO: Latex math
reference for example lecture notes by Herman Bierens
References