cc-Shapley: Measuring Multivariate Feature Importance Needs Causal Context

Explainable artificial intelligence promises to yield insights into relevant features, thereby enabling humans to examine and scrutinize machine learning models or even facilitating scientific discovery. Considering the widespread technique of {Shapley} values, we find that purely data-driven operationalization of multivariate feature importance is unsuitable for such purposes. Even for simple problems with two features, spurious associations due to collider bias and suppression arise from considering one feature only in the observational context of the other, which can lead to misinterpretations. Causal knowledge about the data-generating process is required to identify and correct such misleading feature attributions. We propose cc-{Shapley} (causal context {Shapley}), an interventional modification of conventional observational {Shapley} values leveraging knowledge of the data’s causal structure, thereby analyzing the relevance of a feature in the causal context of the remaining features. We show theoretically that this eradicates spurious association induced by collider bias. We compare the behavior of {Shapley} and cc-{Shapley} values on various, synthetic, and real-world datasets. We observe nullification or reversal of associations when moving from observational to cc-{Shapley}.