Computes standard errors using the expected complete-data information
matrix B from Louis (1982). B = -Hessian(Q), where Q(theta)
is the expected complete-data log-likelihood (the EM Q-function), evaluated at the
converged parameter values with smoothed state probabilities held fixed.
The complete-data information B is typically better conditioned than the
observed-data Hessian. Since I_obs = B - M where M >= 0 is the
missing information, B >= I_obs (PSD), so B^{-1} slightly
underestimates the true variance. The SEs are therefore slightly optimistic but
numerically more stable, especially for weakly identified models.
thetaSE_louis(mdl)List provided as input with additional attributes theta_se, info_mat,
and louis_used = TRUE.
List with model properties (output from an MS model constructor).
Must contain theta, St (smoothed probabilities), and model-specific fields.
Louis, T. A. (1982). "Finding the Observed Information Matrix When Using the EM Algorithm." Journal of the Royal Statistical Society, Series B, 44(2), 226-233.