Sandwich covariance for a 1PL mixed-subjects fit — vcov_mixed_subjects

Estimates the (J+1) × (J+1) sandwich covariance matrix for the shared discrimination and per-item intercepts of a 1PL mixed-subjects calibration.

Usage

vcov_mixed_subjects_1pl(object, ridge = 1e-08, ...)

Arguments

object: A "mixedsubjects_1pl_fit" object from fit_mixed_subjects_1pl() or fit_mixed_subjects_mml_1pl().
ridge: Ridge regularization for Hessian inversion.
...: Unused.

Value

A (J+1) × (J+1) covariance matrix. Row/column names are "a_shared" and "d_Item1", "d_Item2", etc.

Note

Bread approximation. The bread uses avg_hessian_counts_1pl(), the EM complete-data Hessian for the 1PL model, rather than the Louis (1982) marginal observed-information correction implemented for 2PL in vcov_mixed_subjects_mml(). The EM bread over-states efficiency by ignoring missing information about theta. A Louis-corrected 1PL bread is planned for a future release.