Table 1 N (%) of papers that included each of the engagement definition and measurement constructs.

Engagement as a main aim^a

30

39.5

Gave a definition of engagement^b

26

35.1

Objective, e.g., feasibility^b

18

24.3

Subjective, e.g., usability^b

11

14.9

Utility^b

3

4.1

App usage^b

4

5.4

Research protocol

1

1.4

Reported a measure of engagement^a

74

97.4

With the research protocol^b

65

87.8

Objective RMTs^b

64

86.5

Subjective RMTs^b

27

36.5

Combined objective and subjective RMTs^b

22

29.8