Explanation methods applied to sequential models for multivariate time series prediction are receiving more attention in machine learning literature. While current methods perform well at providing instance-wise explanations, they struggle to efficiently and accurately make attributions over long periods of time and with complex feature interactions. We propose WinIT, a framework for evaluating feature importance in time series prediction settings by quantifying the shift in predictive distribution over multiple instances in a windowed setting. Comprehensive empirical evidence shows our method improves on the previous state-of-the-art, FIT, by capturing temporal dependencies in feature importance. We also demonstrate how the solution improves the appropriate attribution of features within time steps, which existing interpretability methods often fail to do. We compare with baselines on simulated and real-world clinical data. WinIT achieves 2.47x better performance than FIT and other feature importance methods on real-world clinical MIMIC-mortality task. The code for this work is available at https://github.com/layer6ai-labs/WinIT.
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