Table 1.

Summary of the trade-offs between requirements, constraints, and resolution.

Research goal	Smartphone constraints	Trade-off	Potential design solution(s)
Readily accessible participant data	Protect user’s privacy by restricting access to data	Data availability versus user privacy	Strict adherence to mobile platform app guidelines captured in a reusable app development kit for app developers
Unified way to collect passive and active data	Smartphone vendor fragmentation creating platform-specific data collection challenges, such as continuous background sensing on Apple devices	High quality data versus Platform and device limitations	Tested and verified implementation for accessing sensor data that wraps platform-specific data collection strategies in a common interface
High resolution data collection strategy (eg, continuous high frequency sampling over many days)	Sensor usage limited to extend battery life Impacts on network responsiveness and user data costs if cellular networks used to upload large data payloads	High resolution data versus poor user experience High resolution data versus additional costs to participant	Custom communication protocol between mobile apps and core platform allows tailoring of frequency and duration of sensor sampling to manage energy and bandwidth impacts for users Platform enforces upper limits on data collection resolution Platform merges and schedules multiple requests to minimize impacts on users’ devices Support for customized scheduling of data uploads (eg, to use only Wi-Fi connectivity)