Tilhliðarlíkan

Tilhliðarlíkan is a secondary or auxiliary model used alongside a primary model to describe aspects of a system that the main model does not capture well, or to aid in estimation of parameters. The term is used in Icelandic statistical and econometric literature as a counterpart to the English term “auxiliary model” or “side model.” It is not meant to replace the main model but to complement it, often by addressing nuisance parameters, measurement error, missing data, or other simplifications.

Common applications include modeling nuisance processes or measurement mechanisms, facilitating two-stage estimation, or enabling data augmentation in Bayesian analyses. For example, an auxiliary model might describe how observed measurements deviate from true values, while the primary model links the true values to outcomes. In practice, the tilhliðarlíkan can provide estimates or constraints that improve identifiability, efficiency, or calibration of the main model. It may also serve as a simpler, tractable description that guides or stabilizes more complex modeling.

Advantages of using a tilhliðarlíkan include better handling of ancillary issues, potential gains in estimation efficiency, and clearer separation of different sources of variation. Limitations include the risk that mis-specification of the auxiliary model biases results, added computational burden, and the need to ensure compatibility between the auxiliary and primary models. The success of this approach depends on thoughtful specification, validation of assumptions, and transparent reporting of how the auxiliary model influences inferences.

Etymology: tilhliðarlíkan combines til hlið (beside, side) with líkan (model), reflecting its role as a model that sits beside the main one.