Private Law Theory

ABSTRACT
Parsimony, as a design principle, is the insight that fewer features may be preferable in many contexts. Features may be redundant; they may offset the effect of other features and they may make little effective contribution to the outcome. Parsimony restrains the impulse to accrete complexity through the addition of features. Adding features increases the risk of overfitting the model to the data on which it is built. Each additional feature in a model compounds the effect of variability. And there is an economy to modeling: the respective contributions of each feature to the overall performance of the model must outstrip the costs to justify the feature’s inclusion. Black letter law – the law we find in Restatements and treatises – are models of law. They specify features for legal consideration (‘factors,’ ‘elements’); the values of those features determine the output of a legal rule. This paper explores the principle of parsimony as applied to legal rules. Recasting legal rules into algorithmic form and subjecting them to testing can reveal the strengths and weaknesses of current legal formulations. Law accretes novel tests and additional considerations, evolving rules that appear to be more precise, yet which burden the law with undesirable complexity. Lawmakers can learn to appreciate elegance in design – a less-is-more notion that praises the achievement of an objective in a way that draws fewer resources. A parsimonious approach to law queries whether every feature’s presence within a legal rule can be justified. By selectively eliminating single features from the model of a rule and then testing the resultant we can reveal opportunities for feature reduction without overly impairing the power of the rule. Parsimony as a general design principle and feature elimination intended to reduce or eliminate algorithmic bias interact. Law, old and new, rejects the introduction of certain features – such as race or gender – into legal rules on policy grounds. Algorithmic bias analysis reveals the reintroduction of these attributes indirectly through feature proxies. Eliminating features that function as conduits of bias can work in parallel with the application of parsimony – although at a certain point our legal models may become too thin to be functional.

Atik, Jeffery, Parsimony – Using Feature Engineering to Critique Private Law Rules (October 21, 2021). Loyola Law School, Los Angeles Legal Studies Research Paper No 2021-28.

First posted 2021-10-25 08:00:07