This arm will receive the arts intervention (any of the arts interventions).

This arm will be the waitlist control and after 3 months it will be active.

Arts (music, cinema, dance).

The Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS). This tool was developed in order to measure mental wellbeing in the general population by Tennant et al. (2007). It consists of 14 items responding using a 5-point Likert scale from 1 (never) to 5 (all the time). The overall score is calculated by summing the responses for every item without reversing none. The minimum overall score ranges from 14 to 70. Higher scores indicate increased mental wellbeing. The scale has been widely used nationally and internationally for monitoring, evaluating projects and programmes and investigating the determinants of mental wellbeing. An efficient internal consistency was proven using Cronbach's alpha score which was 0.89 for the student sample and 0.91 for the general population sample. Also, test-retest reliability at one week was high (0.83). The Greek validation showed acceptable internal consistency (Cronbach's alpha score 0.90).

The Patient Health Questionnaire-9 (PHQ-9) is a questionnaire which measures depression and grade severity of symptoms in general medical and mental health settings using nine DSM-5 criteria for major depression within the last two weeks. PHQ-9 constructed by Kroenke et al. (2001) and validated in Greek by Hyphantis et al. (2011) is using a four-point Likert-type scale. After summing all responses (0=not at all, 3=nearly every day), scores range from 0 to 27, with higher levels indicating increased symptom severity (0-4 no to minimal; 5-9 mild; 10-14 moderate; 15-19 moderately severe; 20-27 severe). The internal reliability of the PHQ-9 was excellent, with a Cronbach's α of 0.89 in the PHQ Primary Care Study (Kroenke et al., 2001) and 0.82 in Greek validation (Hyphantis et al., 2011).

The Generalised Anxiety Disorder Assessment (GAD-7) is provided to screen symptom severity for the four most common anxiety disorders (generalized anxiety disorder, panic disorder, social phobia and posttraumatic stress disorder). GAD-7 constructed by Spitzer et al (2006) and validated in Greek by Vogazianos et al (2022). It consists of 7 items. The GAD-7 score is computed by assigning scores of 0, 1, 2, and 3, to the response categories of 'not at all', 'several days', 'more than half the days', and 'nearly every day', respectively, and summing together the scores for the seven questions (scores range from 0 to 21). Higher levels indicate increased anxiety. There are cut-offs for severity of anxiety as: (i) score 0-4: Minimal Anxiety; (ii) score 5-9: Mild Anxiety; (iii) score 10-14: Moderate Anxiety; (iv) score greater than 15: Severe Anxiety. The internal consistency of the GAD-7 was excellent (Cronbach α = 0.92) (Spitzer et al., 2006).

The Revised UCLA Loneliness Scale-20 (UCLA-20) is a questionnaire which measures level of psychological loneliness experienced by a person. UCLA-20 constructed by Russel et al. (1980) and validated in Greek by Anderson & Malikiosi-Loizos (1992). The internal reliability of the UCLA-20 was excellent, with a Cronbach's α of 0.94 (Russel et al., 1980) and 0.89 in Greek validation (Anderson & Malikiosi-Loizos, 1992). This long scale was shortened to 3 questions (UCLA 3-item Loneliness Scale) in order to be used in large surveys (Hughes et al., 2004). It is using a 3-point Likert-type scale (hard ever, some of the time, often). The scores can be added together to give a range of scores from 3 to 9. Higher scores mean most lonely (worse outcome).