Table 1.

Use and user experience question content (adapted from [18]).

Item	Question content	Impact on nonusage and dropout attrition rate
1	Quality and relevance of information given before the trial	If low, risk of unrealistic expectations which results in a disengagement
2	Ease of the inclusion process (consent, implementation)	Quality of recruitment affects attrition. if it is too easy to enroll then the dropout rate may be high
3	Ease of drop out/stop using it	This parameter can negatively influence the use of the app
4	Ease of use and reliability of the technical interface	Poor usability (complexity of the interaction between an object and its user) contributes to a high rate of attrition
5	“Incentive” or “push” factors (callbacks, reminders, research assistants chasing participants)	This parameter can positively influence the use of the app (staying more in the trial)
6	Personal contact (during registration and inclusion) via face-to-face or by phone, rather than virtual contacts	Human contact promotes the use of the app
7	General quality of the feedback information and of the information summary screen	Positive feedback and encouragement positively influence the use of the app
8	Perceived benefits of interest in completing the study	Motivational factor that decreases attrition
9	Free to use	Paying more commits the user and decreases attrition
10	Time and workload required by the apps	If the burden is too high, it may result in higher attrition
11	Existence of concurrent interventions (web, therapy)	Risk that the user no longer perceives the specific interest of the app
12	Major life events, or of society, which could have stopped using the app	Lead to distraction and nonuse by shifting priorities
13	Experience of the other user (or being able to obtain help)	Indirectly through to dropout and nonusage