Graduation Year


Document Type




Degree Name

Doctor of Philosophy (Ph.D.)


Electrical Engineering

Degree Granting Department

Electrical Engineering

Major Professor

Andrew Raij, Ph.D.

Committee Member

Wilfrido Moreno, Ph.D.

Committee Member

Nasir Ghani, Ph.D.

Committee Member

Carlos Reyes, Ph.D.

Committee Member

Federico Giovannetti, M.S.


Affective Computing, mHealth, Reinforcement Learning, Ubiquitous Computing


A deeper understanding of human physiology, combined with improvements in sensing technologies, is fulfilling the vision of affective computing, where applications monitor and react to changes in affect. Further, the proliferation of commodity mobile devices is extending these applications into the natural environment, where they become a pervasive part of our daily lives. This work examines one such pervasive affective computing application with significant implications for long-term health and quality of life adaptive just-in-time interventions (AJITIs). We discuss fundamental components needed to design AJITIs based for one kind of affective data, namely stress. Chronic stress has significant long-term behavioral and physical health consequences, including an increased risk of cardiovascular disease, cancer, anxiety and depression. This dissertation presents the state-of-the-art of Just-in-time interventions for stress. It includes a new architecture. that is used to describe the most important issues in the design, implementation, and evaluation of AJITIs. Then, the most important mechanisms available in the literature are described, and classified. The dissertation also presents a simulation model to study and evaluate different strategies and algorithms for interventions selection. Then, a new hybrid mechanism based on value iteration and monte carlo simulation method is proposed. This semi-online algorithm dynamically builds a transition probability matrix (TPM) which is used to obtain a new policy for intervention selection. We present this algorithm in two different versions. The first version uses a pre-determined number of stress episodes as a training set to create a TPM, and then to generate the policy that will be used to select interventions in the future. In the second version, we use each new stress episode to update the TPM, and a pre-determined number of episodes to update our selection policy for interventions. We also present a completely online learning algorithm for intervention selection based on Q-learning with eligibility traces. We show that this algorithm could be used by an affective computing system to select and deliver in mobile environments. Finally, we conducts posthoc experiments and simulations to demonstrate feasibility of both real-time stress forecasting and stress intervention adaptation and optimization.