Smartphones have become increasingly pervasive over the past few years and they have clearly transformed the lives of many across the world. On one hand, the smartphone, as a powerful computer on the go, has made many aspects of life and work much easier and accessible. On the other hand, the always-on always-connected devices have also brought problems such as technology addiction, making sedentary lifestyle even more prevalent. Thus we are motivated to explore both the negative and positive aspects of smartphones in this dissertation work.
Although current research on smartphone addiction has mainly focused on addiction at the device level, we are the first to explore, more specifically, app addiction. In the first part of the thesis, we investigated smartphone usage for college students using surveys, logged data, and interviews. Specifically, we adapted existing smartphone addiction assessment instruments to measure app addiction. The analysis of our data shows that social and communication apps are the top 2 most addictive categories among participants. Female and male participants show no significant difference in terms of smartphone addiction. However, female participants tend to report that they are addicted to more apps. The psychological factors associated with app addiction are different between app categories. For example, compared to communication apps, participants report that it is easier to withdraw from social apps, but more difficult to control time spent on them. Correlation analysis between app usage features and app addictiveness scores reveals that compulsive open times, usage duration, and regularity of usage are good indicators of app addiction, though response time to notifications has limited predictive power.
In the second part of this dissertation, we designed and implemented a just-in-time health intervention system, which uses rich context extracted from a smart-phone and smart watch to encourage opportunistic walking without significantly altering users' daily schedules. To develop a smart health intervention system, we abstracted and implemented a context-aware reminder triggering(CART) framework on Android platform which features easy integration with external devices, rich expressiveness in rule definitions, flexibility in rule engine configuration and support of multi-modal interventions. To make our intervention strategy more effective, we also incorporated several existing psychological theories such as Behavior Change Theory, Habit Formation Theory and Goal Setting Theory into our system. To validate the effectiveness of our intervention system, we conducted a 4-weeks' user study. The results of the study show our health intervention system is effective in encouraging people to walk more and engage other physical activities. Compared with reminders sent randomly in time, context-aware reminders are more acceptable to participants and more effective in increasing participants' self-awareness of possible walking opportunities.