TReating Unhelpful Suspicious Thoughts in Adolescents (TRUST): a School-based Case Series

GREEN: > 5 participants of target recruited AMBER = 3 to 4 of target recruited RED < 2 of target recruited

GREEN: 5 or more of participants providing end of therapy assessment outcome data AMBER: 3 to 4 participants providing end of therapy assessment outcome data RED: 2 or less of participants providing end of therapy assessment outcome data

GREEN= 5 or more participants attend at least 3 sessions of therapy AMBER>= 3 to 4 participants attend at least 3 sessions of therapy RED: 2 or less of participants attend at least 3 sessions of therapy

Acceptability of the therapy will be assessed via therapy process feedback questionnaire given to participants upon therapy completion or withdrawal and adverse effects of study participation questionnaire.

For screening of and assessing adolescents' paranoia, Revised Green et al., Paranoid Thoughts Scale (R-GPTS) will be used due to high reliability. The R-GPTS comprises of two subscales assessing for frequency of ideas of references (eight questions) and ideas of persecution (10 questions) on a five-point Likert scale. Part B will be used. "The R-GPTS score ranges are: average (Reference: 0-9; Persecution: 0-4); elevated (Reference: 10-15; Persecution: 5-10); moderately severe (Reference: 16-20; Persecution:11-17); severe (Reference: 21-24; Persecution: 18-27); and very severe (Reference: 25+; Persecution: 28+)". Clinical cut-offs on the persecution scales are 11 for persecutory ideation. Higher levels of RGPTs scores indicate higher difficulties.

The compACT-Y consists of 19-items scored on a six-point likert scale to assess psychological flexibility, with higher scores indicating higher flexibility. This includes the three factors of valued action, openness to experience and behavioural awareness, all linking to acceptance and commitment therapy (ACT) frameworks and methodology. This has been identified to be a valid and reliable measure for the use in young people.

The MIQ-N consists of 16-items assessing for experiences of mental images. It has four sub-scales: intrusiveness, realness, controllability and beliefs about mental imagery. Participants are asked to rate how true each of the statements are to them on a seven-point Likert scale. Cronbach's alpha ranges from 0.84 - 0.90 when each of the subscales have been tested for reliability. The higher the score the higher the experience of negative mental images.

The BCSS evaluates self and other beliefs using a 24-item scale, rating positive and negative self and other beliefs. Participants are asked to initially rate whether they hold the belief on yes/no and then rate the strength of the belief using a four-point Likert scale. Negative evaluations of self and others are suggested to be indicative of paranoia in the general population. The measure has good internal consistency for non-clinical samples (α = 0.74) and good retest-reliability for all subscales.

The WSAS-Y is a measure of functionality for young people in areas such as school, relationships and activities. It has five subscales and assesses severity of impairment using an eight-point scale, generating a total score out of 40, with greater scores indicating greater impairment. It has been suggested to have high internal consistency (α = 0.84) and reliability (r = 0.80).

The weekly imagery characteristics scale is a seven-item measure rating the characteristics of mental images including how real or pre-occupying they are. Participants are asked to rate each item on a 10-point scale from 'not at all' to 'extremely'.