Table 1.

Coding strategy.

Main steps	Used approach
Creating the category system
Basic strategy	Deductive-inductive
Deductive categorization	Initial interviews: - Use of digital devices in general - First impression of the DoctorME app - Perceived usability - Usage behaviour - Expectations	Post-interviews: - Perceived usability - Perceived benefit - Usage behaviour/experiences - Self-care of heart failure - Recommendation of the DoctorME app - Voluntary monthly costs - Artificial intelligence recommendations on medications
Inductive categorization	Subsumption
Persons involved	2 (health scientists, medical informatician)
Termination criterion	None
Division of material
Unit	Coding unit
Coding unit	Individual words and phrases
Systematic	Marking and coding in one step
Persons involved	1
Coding
Test coding	Yes
Person involved in main coding	2