Table 2

Summary of the outcome measures

Outcome measure	Questions (n)	Type of outcome	Frequency	Scoring	Details of assessment
Primary measure
Difficulties in Emotion Regulation Scale-860	8	Primary outcome	All timepoints	8–40 (higher=more difficulties)	Difficulties associated with response to situations eliciting negative emotions.
Mental health measures
Self-Harm Questionnaire (SHQ) screening questions63	3	Mental health	All timepoints	Analysed separately	Frequency and risk of self-harm thoughts, suicidal ideation and behaviour.
SHQ additional items63	22	Covariate	Once (baseline)	Analysed separately	4 dimensions of self-harm (NSSI, suicide attempts, suicide threats, suicide ideation).
Generalised Anxiety Disorder Questionnaire-764	7	Mental health	All timepoints	0–21 (higher=greater severity)	Presence and severity of generalised anxiety disorder.
Patient Health Questionnaire65	9	Mental health	All timepoints	0–27 (higher=greater severity)	Severity of depressive symptoms.
Proximal and mechanistic measures
Process Model of Emotion Regulation Questionnaire66	9	Mechanistic	3 timepoints	2 subscales Average across each subscale, higher=greater endorsement.	Attentional deployment subscales; focus on engagement and disengagement.
State Hope Scale67	6	Proximal	3 timepoints	6–48 (higher=greater state hopefulness)	Goal-directed thinking; agency and pathways.
UCLA Loneliness Scale for children68	3	Proximal	3 timepoints	3–12 (higher=more loneliness)	Subjective feelings of loneliness.
Engagement measures
Bespoke Purrble questions59	7	Engagement	Deployment	Analysed separately	Purrble use and perceived usefulness.
TWente Engagement with Ehealth Technologies Scale69	9	Engagement	Deployment	3 subscales Total score per subscale=greater engagement	Engagement with intervention device; behavioural, cognitive and affective engagements.

Note: UCLA= University of California, Los Angeles; NSSI = Non-Suicidal Self-Injury