Table 1.

Reasons for dropout across studies.

Reason for dropout	Frequency	Related theme
Lost or stolen smartphone	23	Usability
Technical malfunction (eg, smartphone corrupted, not receiving texts, or delivery delays)	7	Usability
Exacerbation of health condition, including participants who were injured or died during the course of the study	6	Health status
Deleted app	3	Usability
App not compatible with existing smartphone	3	Convenience and accessibility
Unexpected usage patterns (eg, switched smartphone off in between answering surveys, left smartphone plugged into charger, used smartphone in airplane mode)	3	Perceived utility
Moved out of area or was discharged from hospital	3	Convenience and accessibility
Sold smartphone	2	Perceived utility
Changed mobile phone or service plan	2	Convenience and accessibility
Practical technical difficulties (eg, not being able to download the app)	2	Usability
Broken smartphone	1	Usability
Inconsistent wireless network	1	Convenience and accessibility
App consumed too much battery	1	Usability
System too slow	1	Usability
Unspecified reason	11	Not applicable