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Alexander Van Esbroeck

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3 papers
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3

JMLR Journal 2016 Journal Article

Monotonic Calibrated Interpolated Look-Up Tables

  • Maya Gupta
  • Andrew Cotter
  • Jan Pfeifer
  • Konstantin Voevodski
  • Kevin Canini
  • Alexander Mangylov
  • Wojciech Moczydlowski
  • Alexander Van Esbroeck

Real-world machine learning applications may have requirements beyond accuracy, such as fast evaluation times and interpretability. In particular, guaranteed monotonicity of the learned function with respect to some of the inputs can be critical for user confidence. We propose meeting these goals for low-dimensional machine learning problems by learning flexible, monotonic functions using calibrated interpolated look-up tables. We extend the structural risk minimization framework of lattice regression to monotonic functions by adding linear inequality constraints. In addition, we propose jointly learning interpretable calibrations of each feature to normalize continuous features and handle categorical or missing data, at the cost of making the objective non-convex. We address large- scale learning through parallelization, mini-batching, and random sampling of additive regularizer terms. Case studies on real-world problems with up to sixteen features and up to hundreds of millions of training samples demonstrate the proposed monotonic functions can achieve state-of-the-art accuracy in practice while providing greater transparency to users. [abs] [ pdf ][ bib ] &copy JMLR 2016. ( edit, beta )

AIIM Journal 2015 Journal Article

Predicting readmission risk with institution-specific prediction models

  • Shipeng Yu
  • Faisal Farooq
  • Alexander Van Esbroeck
  • Glenn Fung
  • Vikram Anand
  • Balaji Krishnapuram

Objective The ability to predict patient readmission risk is extremely valuable for hospitals, especially under the Hospital Readmission Reduction Program of the Center for Medicare and Medicaid Services which went into effect starting October 1, 2012. There is a plethora of work in the literature that deals with developing readmission risk prediction models, but most of them do not have sufficient prediction accuracy to be deployed in a clinical setting, partly because different hospitals may have different characteristics in their patient populations. Methods and materials We propose a generic framework for institution-specific readmission risk prediction, which takes patient data from a single institution and produces a statistical risk prediction model optimized for that particular institution and, optionally, for a specific condition. This provides great flexibility in model building, and is also able to provide institution-specific insights in its readmitted patient population. We have experimented with classification methods such as support vector machines, and prognosis methods such as the Cox regression. We compared our methods with industry-standard methods such as the LACE model, and showed the proposed framework is not only more flexible but also more effective. Results We applied our framework to patient data from three hospitals, and obtained some initial results for heart failure (HF), acute myocardial infarction (AMI), pneumonia (PN) patients as well as patients with all conditions. On Hospital 2, the LACE model yielded AUC 0. 57, 0. 56, 0. 53 and 0. 55 for AMI, HF, PN and All Cause readmission prediction, respectively, while the proposed model yielded 0. 66, 0. 65, 0. 63, 0. 74 for the corresponding conditions, all significantly better than the LACE counterpart. The proposed models that leverage all features at discharge time is more accurate than the models that only leverage features at admission time (0. 66 vs. 0. 61 for AMI, 0. 65 vs. 0. 61 for HF, 0. 63 vs. 0. 56 for PN, 0. 74 vs. 0. 60 for All Cause). Furthermore, the proposed admission-time models already outperform the performance of LACE, which is a discharge-time model (0. 61 vs. 0. 57 for AMI, 0. 61 vs. 0. 56 for HF, 0. 56 vs. 0. 53 for PN, 0. 60 vs. 0. 55 for All Cause). Similar conclusions can be drawn from other hospitals as well. The same performance comparison also holds for precision and recall at top-decile predictions. Most of the performance improvements are statistically significant. Conclusions The institution-specific readmission risk prediction framework is more flexible and more effective than the one-size-fit-all models like the LACE, sometimes twice and three-time more effective. The admission-time models are able to give early warning signs compared to the discharge-time models, and may be able to help hospital staff intervene early while the patient is still in the hospital.

AAAI Conference 2012 Conference Paper

Heart Rate Topic Models

  • Alexander Van Esbroeck
  • Chih-Chun Chia
  • Zeeshan Syed

A key challenge in reducing the burden of cardiovascular disease is matching patients to treatments that are most appropriate for them. Different cardiac assessment tools have been developed to address this goal. Recent research has focused on heart rate motifs, i. e. , short-term heart rate sequences that are overor under-represented in long-term electrocardiogram (ECG) recordings of patients experiencing cardiovascular outcomes, which provide novel and valuable information for risk stratification. However, this approach can leverage only a small number of motifs for prediction and results in difficult to interpret models. We address these limitations by identifying latent structure in the large numbers of motifs found in long-term ECG recordings. In particular, we explore the application of topic models to heart rate time series to identify functional sets of heart rate sequences and to concisely describe patients using task-independent features for various cardiovascular outcomes. We evaluate the approach on a large collection of real-world ECG data, and investigate the performance of topic mixture features for the prediction of cardiovascular mortality. The topics provided an interpretable representation of the recordings and maintained valuable information for clinical assessment when compared with motif frequencies, even after accounting for commonly used clinical risk scores.

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