Early Exit Ensembles for Uncertainty Quantification
Alexander Campbell*, Lorena Qendro*, Pietro Lio, Cecilia Mascolo
Abstract: Deep learning is increasingly used for decision-making in health applications. However, commonly used deep learning models are deterministic and are therefore unable to provide any estimate of predictive uncertainty. Quantifying model uncertainty is crucial for reducing the risk of misdiagnosis by informing practitioners of low-confident predictions. To address this issue, we propose early exit ensembles, a novel framework capable of capturing predictive uncertainty via an implicit ensemble of early exits. We evaluate our approach on the task of classification using three state-of-the-art deep learning architectures applied to three medical imaging datasets. Our experiments show that early exit ensembles provide better-calibrated uncertainty compared to Monte Carlo dropout and deep ensembles using just a single forward pass of the model. Depending on the dataset and baseline, early exit ensembles can improve uncertainty metrics up to 2x, while increasing accuracy by up to 2% over its deterministic counterpart. Finally, our results suggest that by providing well-calibrated predictive uncertainty for both in- and out-of-distribution inputs, early exit ensembles have the potential to improve trustworthiness of models in high-risk medical decision-making.