cs.LGFeb 18, 2026

Interpretability-by-Design with Accurate Locally Additive Models and Conditional Feature Effects

Authors: Vasilis Gkolemis, Loukas Kavouras, Dimitrios Kyriakopoulos, Konstantinos Tsopelas, Dimitrios Rontogiannis, Giuseppe Casalicchio, Theodore Dalamagas, Christos Diou

Organizations: ATHENA RC, Greece · HUA, Greece · Max Planck ISS, Germany · LMU, Germany

Abstract

Generalized additive models (GAMs) offer interpretability through independent univariate feature effects but underfit when interactions are present in data. GA2^2Ms add selected pairwise interactions which improves accuracy, but sacrifices interpretability and limits model auditing. We propose Conditionally Additive Local Models (CALMs), a new model class, that balances the interpretability of GAMs with the accuracy of GA2^2Ms. CALMs allow multiple univariate shape functions per feature, each active in different regions of the input space. These regions are defined independently for each feature as simple logical conditions (thresholds) on the features it interacts with. As a result, effects remain locally additive while varying across subregions to capture interactions. We further propose a principled distillation-based training pipeline that identifies homogeneous regions with limited interactions and fits interpretable shape functions via region-aware backfitting. Experiments on diverse classification and regression tasks show that CALMs consistently outperform GAMs and achieve accuracy comparable with GA2^2Ms. Overall, CALMs offer a compelling trade-off between predictive accuracy and interpretability.

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