Symptom Assessment

Six types of psychotic experiences were assessed: paranoia, hallucinations, cognitive disorganization, grandiosity, anhedonia, all via self-report, and negative symptoms via parent report. The online supplementary appendix provides further details. Paranoia was assessed with 15 items from the Paranoia Checklist.^{21 (link)}Hallucinations were assessed with 9 items from the Cardiff Anomalous Perceptions Scale.^{26 (link)}Cognitive disorganization was assessed with 11 items from the short Oxford-Liverpool Inventory of Feelings and Experiences.^{27 (link)}Grandiosity was assessed with items from the “Myself” subscale of Cognition Checklist for Mania-Revised,^{28 (link)} the Peters and colleagues’ Delusions Inventory,^{29 (link)} and items developed from clinical case studies. Anhedonia was assessed with 10 items from the anticipatory pleasure subscale of the Temporal Experience of Pleasure Scale³⁰ (the scale was reversed so that higher scores indicated more anhedonia). Parent-rated negative symptoms were assessed with 10 items devised from the Scale for the Assessment of Negative Symptoms.³¹ For negative symptoms, both self-report and rater (parent) report were employed, in line with recent recommendations.^{32 (link)}Finally, distress was assessed with an item at the end of each of the paranoia, hallucinations, cognitive disorganization, and grandiosity subscales.

The Adjustment Disorder New Module-8 Child and Adolescent Version (ADNM-8-CA) will be used to measure exposure to stressors in the past month and ICD-11 symptoms of adjustment disorder [1 , 20 (link)]. The ADNM-8-CA stressors list includes 16 potentially stressful events relevant to adolescents (e.g. parents’ divorce, difficulties in school, the end of the friendship). Participants are asked to provide binary answers No or Yes if they have experienced any of the listed stressors over the last 12 months. The assessment of adjustment disorder symptoms includes eight symptom items. The ADNM-8-CA measures two ICD-11 adjustment disorder symptoms: (1) preoccupation with the stressor (4 items) and (2) failure to adapt (4 items). A 4-point Likert scale, ranging from Never (= 1) to Often (= 4) is used to evaluate the frequency of the listed symptoms. The total score of the ADNM-8-CA range from 1 to 32. A higher total score which is a sum of all the ADNM-8-CA symptom items, indicates higher adjustment problems, and a score ≥ 23 indicates probable adjustment disorder. The ADNM-8-CA was previously used in a large Lithuanian adolescent sample, and good psychometric properties have been reported [1 ].
The Generalized Anxiety Disorder-7 (GAD-7) [21 ] will be used to measure generalized anxiety symptoms that bothered participants during the past 2 weeks. The GAD-7 comprises 7 items with the possible answers ranging on a 4-point Likert scale from Not at all (= 0) to Nearly every day (= 3). The total score of the GAD-7 range from 0 to 21, with higher scores indicating higher generalized anxiety problems. The GAD-7 is applicable to adolescents from 12 years old. However, GAD-7 has not previously been used in a sample of Lithuanian adolescents. Nevertheless, the GAD-7 showed good psychometric properties in adult samples in Lithuania [22 , 23 ].
The Patient Health Questionnaire-9 (PHQ-9) [24 (link)] will be used to measure depressive symptoms that bothered participants during the past 2 weeks. The PHQ-9 comprises nine items, with the answers ranging from Not at all (= 0) to Nearly every day (= 3) on a 4-point Likert scale. The total score of the PHQ-9 may range from 0 to 27, with higher scores indicating higher depressive symptoms. The PHQ-9 is suitable for adolescents from 13 years old. The PHQ-9 has not been used in a sample of Lithuanian adolescents previously. The PHQ-9, used in adult samples in Lithuania, showed good psychometric properties [22 , 23 ].
The WHO-5 Well-being Index (WHO-5) [25 (link)] will be used to measure general psychological well-being. The WHO-5 comprises five items measuring how an individual felt over the past 2 weeks with a Likert scale ranging At no time (= 0) to All of the time (= 5). The total score of the WHO-5 is the sum of all items multiplied by 4, and may range from 0 to 100, with a bigger score indicating higher well-being. The WHO-5 is suitable for children aged 9 and above. In Lithuanian adult samples, the WHO-5 has good psychometric properties [22 , 23 ].
The Perceived Positive Social Support Scale (PPSS) [26 ] is a revised version of the Crisis Support Scale [27 (link)] measuring social support. The PPSS comprises four items, covering how the participant feels with family and friends (e.g., how often someone tends to listen when the participant wants to talk). Participants are asked to provide a response to each item on an 8-point Likert scale ranging from Never (= 0) to Always (= 7). The total score of PPSS may range from 0 to 28, with higher scores indicating higher perceived positive social support. The PPSS has been used previously in the adolescent sample in Lithuania and showed good psychometric properties [26 ].

Previously published literature for passively sensed behavioral measures [9 (link)] has suggested that the passive sensing data within a particular time frame need to be present in sufficient quantities to rule out cases where sensors were not collecting data in a continuous fashion for some reason (eg, criteria of 3 days out of a week and 18 unique hours per day [9 (link)]). Because human-smartphone interaction sensing will only produce data when participants are actively interacting with the phone, obtaining active data for 24 hours is unlikely; therefore, we relaxed the selection criteria for passive sensing data to at least 3 unique hours per day and at least 3 unique days within the 14-day window per DSM L1 measurement.
As a result, the sample that was entered into the multilevel modeling analysis had 142 participants and 984 measurements of depressive symptoms, where each assessment of depressive symptoms had at least 3 different days and 3 different hours of phone interaction data per day prior to the DSM L1 measurement (totaling 12,098 person-days and 196,673 person-hours).