Learning to Maximize Mutual Information for Dynamic Feature Selection
Ian Connick CovertWei QiuMingyu LuNayoon KimNathan J. WhiteSu-In Lee
Proposes an amortized optimization framework for dynamic feature selection that directly learns greedy conditional mutual information policies from standard labeled data, bypassing the instability of reinforcement learning and the cost of generative modeling.
In many practical machine learning settings, acquiring input features is expensive, time-consuming, or operationally constrained. For instance, in an emergency department, collecting exhaustive diagnostic tests for every patient can cause critical delays. Standard machine learning models use static feature selection, requiring the exact same set of variables for every case. Dynamic feature selection improves on this by sequentially querying only the most relevant features based on the information gathered so far. However, existing methods for dynamic selection—such as reinforcement learning or complex generative modeling—are notoriously unstable, slow to train, and frequently underperform static approaches.
The article develops and evaluates a simple and efficient learning framework for dynamic feature selection. The primary objective is to demonstrate that an amortized optimization approach, which trains a neural network policy to directly predict the greedy feature that maximizes conditional mutual information with the target outcome, consistently outperforms existing static and dynamic baselines.
The researchers formulated a variational perspective showing that selecting the feature with the highest conditional mutual information is equivalent to minimizing the immediate one-step-ahead prediction loss. To make this tractable, they trained two neural networks jointly: a predictor network that classifies outcomes from available features, and a policy network that selects the next best feature. They employed amortized optimization combined with a continuous relaxation (the Concrete distribution) to optimize the discrete selection process efficiently using standard gradient descent. The approach was validated across six tabular datasets—including three clinical emergency medicine cohorts covering 14,463 admissions over a 13-year period (bleeding risk, respiratory support, and fluid responsiveness) and three public benchmarks—as well as two benchmark image classification datasets (MNIST and CIFAR-10).
The evaluation yielded several key findings. First, the proposed greedy method consistently outperformed both static and dynamic baselines across all six tabular datasets across budgets of 1 to 10 features. Second, the performance advantage was most pronounced at low feature budgets; for example, on the MNIST benchmark, the proposed method achieved nearly 90% classification accuracy with only 10 selected pixels, outperforming the best baseline by roughly 10 percentage points. Third, existing dynamic alternatives—such as reinforcement learning via Opportunistic Learning and generative models via partial variational autoencoders—consistently underperformed strong static baselines like the Concrete Autoencoder. Finally, the proposed method substantially reduced computational overhead at inference time, requiring only k forward passes to select k features instead of the computationally prohibitive evaluations required by iterative estimators.
These findings demonstrate that dynamic feature selection does not require complex reinforcement learning pipelines to achieve superior results. By framing dynamic selection around greedy information gain, organizations can drastically reduce data acquisition costs and decision latency without sacrificing predictive performance. In high-stakes environments such as healthcare, this translates to faster risk stratification, reduced testing burden on patients, and improved clinical throughput.
Organizations should adopt this amortized greedy approach when deploying models in workflows where input acquisition is sequential and costly. Future implementations should focus on incorporating non-uniform feature costs, developing adaptive stopping rules that select feature budgets on a per-instance basis, and exploring specialized architectures for complex, partially observed structured inputs.
Confidence in these findings is high for structured tabular and standardized image classification tasks under fixed budgets and uniform feature costs. However, caution is warranted in deployment environments where individual feature acquisition costs differ substantially or where data distributions shift significantly from the training baseline, as the current experiments assumed uniform costs and fixed query budgets.
- Paper: Feature selection based on mutual information criteria of max-dependency, max-relevance, and min-redundancy, Hanchuan Peng et al. (2003). Its incremental mutual-information criterion for balancing target relevance against redundancy provides the information-theoretic foundation for understanding the source’s conditional mutual-information feature choices.
- Paper: Toward Optimal Feature Selection, Daphne Koller et al. (1996). Its use of conditional independence and information loss to eliminate features prepares readers for the source’s conditional mutual-information objective.
- Paper: Feature Selection: Evaluation, Application, and Small Sample Performance, Anil K. Jain et al. (1997). Its comparison of feature-selection strategies clarifies the static-selection baseline that the source contrasts with sequential, instance-specific querying.
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