Patrick Emedom-Nnamdi

2025

1. AOAS

   

   Nonparametric Additive Value Functions: Interpretable Reinforcement Learning with an Application to Surgical Recovery

   Patrick Emedom-Nnamdi, Timothy R. Smith, Jukka-Pekka Onnela, and Junwei Lu

   Annals of Applied Statistics, 2025

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   We propose a nonparametric additive model for estimating interpretable value functions in reinforcement learning, with an application in optimizing postoperative recovery through personalized, adaptive recommendations. While reinforcement learning has achieved significant success in various domains, recent methods often rely on black-box approaches, such as neural networks, which hinder the examination of individual feature contributions to a decision-making policy. Our novel method offers a flexible technique for estimating action-value functions without explicit parametric assumptions, overcoming the limitations of the linearity assumption of classical algorithms. By incorporating local kernel regression and basis expansion, we obtain a sparse, additive representation of the action-value function, enabling local approximation and retrieval of nonlinear, independent contributions of select state features and the interactions between joint feature pairs. We validate our approach through a simulation study and apply it to spine disease recovery, uncovering recommendations aligned with clinical knowledge. This method bridges the gap between flexible machine learning techniques and the interpretability required in healthcare applications, paving the way for more personalized interventions.

2. PLOS Digital Health

   Design and feasibility of smartphone-based digital phenotyping for long-term mental health monitoring in adolescents

   D. Huang, P. Emedom-Nnamdi, J. P. Onnela, and A. Van Meter

   PLOS Digital Health, 2025

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   Assessment of psychiatric symptoms relies on subjective self-report, which can be unreliable. Digital phenotyping collects data from smartphones to provide near-continuous behavioral monitoring. It can be used to provide objective information about an individual’s mental state to improve clinical decision-making for both diagnosis and prognostication. The goal of this study was to evaluate the feasibility and acceptability of smartphone-based digital phenotyping for long-term mental health monitoring in adolescents with bipolar disorder and typically developing peers. Participants (aged 14–19) with bipolar disorder (BD) or with no mental health diagnoses were recruited for an 18-month observational study. Participants installed the Beiwe digital phenotyping app on their phones to collect passive data from their smartphone sensors and thrice-weekly surveys. Participants and caregivers were interviewed monthly to assess changes in the participant’s mental health. Analyses focused on 48 participants who had completed participation. Average age at baseline was 15.85 years old (SD = 1.37). Approximately half (54%) identified as female, and 54% identified with a minoritized racial/ethnic background. Completion rates across data types were high, with 99% (826/835) of clinical interviews completed, 89% of passive data collected (22,233/25,029), and 47% (4,945/10,448) of thrice-weekly surveys submitted. The proportion of days passive data were collected was consistent over time for both groups; the clinical interview and active survey completion decreased over the study course. Results of this study suggest digital phenotyping has significant potential as a method of long-term mental health monitoring in adolescents. In contrast to traditional methods, including interview and self-report, it is lower burden and provides more complete data over time. A necessary next step is to determine how well the digital data capture changes in mental health to determine the clinical utility of this approach.

3. Cancers

   A Digital Phenotypic Assessment in Neuro-Oncology (DANO): A Pilot Study on Sociability Changes in Patients Undergoing Treatment for Brain Malignancies

   F. Siddi, P. Emedom-Nnamdi, M. P. Catalino, A. Rana, A. Boaro, H. Y. Dawood, F. Sala, J.-P. Onnela, and T. R. Smith

   Cancers, 2025

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   Background: The digital phenotyping tool has great potential for the deep characterization of neurological and quality-of-life assessments in brain tumor patients. Phone communication activities (details on call and text use) can provide insight into the patients’ sociability. Methods: We prospectively collected digital-phenotyping data from six brain tumor patients. The data were collected using the Beiwe application installed on their personal smartphones. We constructed several daily sociability features from phone communication logs, including the number of incoming and outgoing text messages and calls, the length of messages and duration of calls, message reciprocity, the number of communication partners, and number of missed calls. We compared variability in these sociability features against those obtained from a control group, matched for age and sex, selected among patients with a herniated disc. Results: In brain tumor patients, phone-based communication appears to deteriorate with time, as evident in the trend for total outgoing minutes, total outgoing calls, and call out-degree. Conclusions: These measures indicate a possible decrease in sociability over time in brain tumor patients that may correlate with survival. This exploratory analysis suggests that a quantifiable digital sociability phenotype exists and is comparable for patients with different survival outcomes. Overall, assessing neurocognitive function using digital phenotyping appears promising.

4. Neurosurgery

   Assessing Mobility in Patients With Glioblastoma Using Digital Phenotyping—Piloting the Digital Assessment in Neuro-Oncology

   Noah L. A. Nawabi, Patrick Emedom-Nnamdi, John L. Kilgallon, Jakob V. E. Gerstl, David J. Cote, Rohan Jha, Jacob G. Ellen, Krish M. Maniar, Christopher S. Hong, Hassan Y. Dawood, and 2 more authors

   Neurosurgery, 2025

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   BACKGROUND AND OBJECTIVES: Digital phenotyping (DP) enables objective measurements of patient behavior and may be a useful tool in assessments of quality-of-life and functional status in neuro-oncology patients. We aimed to identify trends in mobility among patients with glioblastoma (GBM) using DP. METHODS: A total of 15 patients with GBM enrolled in a DP study were included. The Beiwe application was used to passively collect patient smartphone global positioning system data during the study period. We estimated step count, time spent at home, total distance traveled, and number of places visited in the preoperative, immediate postoperative, and late postoperative periods. Mobility trends for patients with GBM after surgery were calculated by using local regression and were compared with preoperative values and with values derived from a nonoperative spine disease group. RESULTS: One month postoperatively, median values for time spent at home and number of locations visited by patients with GBM decreased by 1.48 h and 2.79 locations, respectively. Two months postoperatively, these values further decreased by 0.38 h and 1.17 locations, respectively. Compared with the nonoperative spine group, values for time spent at home and the number of locations visited by patients with GBM 1 month postoperatively were less than control values by 0.71 h and 2.79 locations, respectively. Two months postoperatively, time spent at home for patients with GBM was higher by 1.21 h and locations visited were less than nonoperative spine group values by 1.17. Immediate postoperative values for distance traveled, maximum distance from home, and radius of gyration for patients with GBM increased by 0.346 km, 2.24 km, and 1.814 km, respectively, compared with preoperative values. CONCLUSIONS: Trends in patients with GBM mobility throughout treatment were quantified through the use of DP in this study. DP has the potential to quantify patient behavior and recovery objectively and with minimal patient burden.

2023

1. RRL 2023

   

   Knowledge Transfer from Teachers to Learners in Growing-Batch Reinforcement Learning

   Patrick Emedom-Nnamdi, Abram L. Friesen, Bobak Shahriari, Nando Freitas, and Matt W. Hoffman

   International Conference on Learning Representations (ICLR) – Reincarnating RL Workshop, 2023

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   Standard approaches to sequential decision-making exploit an agent’s ability to continually interact with its environment and improve its control policy. However, due to safety, ethical, and practicality constraints, this type of trial-and-error experimentation is often infeasible in many real-world domains such as healthcare and robotics. Instead, control policies in these domains are typically trained offline from previously logged data or in a growing-batch manner. In this setting a fixed policy is deployed to the environment and used to gather an entire batch of new data before being aggregated with past batches and used to update the policy. This improvement cycle can then be repeated multiple times. While a limited number of such cycles is feasible in real-world domains, the quality and diversity of the resulting data are much lower than in the standard continually-interacting approach. However, data collection in these domains is often performed in conjunction with human experts, who are able to label or annotate the collected data. In this paper, we first explore the trade-offs present in this growing-batch setting, and then investigate how information provided by a teacher (i.e., demonstrations, expert actions, and gradient information) can be leveraged at training time to mitigate the sample complexity and coverage requirements for actor-critic methods. We validate our contributions on tasks from the DeepMind Control Suite.