Evaluation of the Efficacy of Two Internet-based Self-help Interventions for Loneliness.

Measured with the UCLA Loneliness Scale, 9-Item Version (UCLA-9). Total score ranging from 1-4 (representing the mean score of all 9 items). Lower scores represent less loneliness and a more favourable outcome.

Measured with the Patient Health Questionnaire (PHQ-9). Total score ranging from 0-27 (representing the sum of each of the 9 individual items). Clinical cut-offs for mild, moderate, moderately severe and severe major depressive disorder are considered to be 5, 10, 15, and 20 points.

Measured with the Satisfaction with Life Scale (SWLS). Total score ranging from 1-7 (representing the mean score of all 5 items). Higher scores indicate higher satisfaction with life.

Measured with the subscale "Misanthropy" of the Embitterment Scale (BVI). Total score ranging from 0-4 (representing the mean score of all 5 items). Higher scores indicate a higher degree in misanthropy.

Measured with the Self-Stigma in Loneliness Questionnaire. Total score ranging from 1-5 (representing the mean score of all 6 items). Higher scores indicate higher self-stigma.

Measured with the Social Interaction Anxiety Scale, 6-Item Version (SIAS-6). Total score ranging from 0-5 (representing the mean score of all 6 items) Higher scores indicate higher social interaction anxiety.

Measured with the Social Phobia Scale, 6-Item Version (SPS-6). Total score ranging from 0-5 (representing the mean score of all 6 items). Higher scores indicate higher social phobia.

Measured with the Sussex Oxford Compassion for the Self Scale (SOCS-S). Total score ranging from 1-5 (representing the mean score of all 20 items). Higher scores indicate higher self-compassion.

Measured with the Social Network Index (SNI). Network Diversity ranging from 1-8 (representing the number of social roles in which the respondent has regular contact with at least one person). Higher scores indicate a more diverse social network. Number of people in Social Network ranging from 0 to infinity. Higher scores indicate a larger social network.

Measured with the Interpretation and Judgmental Questionnaire (IJQ). The interpretation score ranges from 1-4 (representing the chosen likelihood of the profoundly negative alternative). Higher scores indicate more negatively biased processing.

Measured with the Rejection Sensitivity Questionnaire (A-RSQ). Total score ranging from 1-36 (representing the mean score of the multiplication of the subscales of all 9 items). Higher scores indicate higher rejection sensitivity.

Measured with the "behavioral-social avoidance"-subscale of the Cognitive-Behavioral Avoidance Scale (CBAS). Total score ranging from 1-5 (representing the mean score of all 8 items). Higher scores indicate higher behavioral-social avoidance.

Measured with the Distress Disclosure Index (DDI). Total score ranging from 1-5 (representing the mean score of all 12 items). Higher scores indicate higher levels of distress disclosure.

Measured with the Kernis-Goldman Authenticity Inventory - Short Form (KGAI-SF). Total score ranging from 1-5 (representing the mean score of all 20 items). Higher scores indicate less authenticity.

Measured with the Inventory for the Assessment of Negative Effects of Psychotherapy (INEP). Total score ranging from -3-3 (representing the mean score of all items). Higher scores indicate less unfavourable effects of psychotherapy.

Measured with the Client Satisfaction Questionnaire (ZUF-8). Total score ranging from 1-4 (representing the mean score of all 8 items). Higher scores indicate higher client satisfaction.

Measured with the System Usability Scale (SUS). Total score ranging from 0-100 (representing the sum score multiplied by 2.5). Higher scores indicate higher perceived usability.

Measured with the Rosenberg Self-Esteem Scale (RSES). Total score ranging from 0-30 (representing the sum of each of the 10 individual items). Higher scores indicate higher self-esteem.

Measured with the subscale "self-determined motivation for solitude" of the Motivation for Solitude Scale - Short Form (MSS-SF). Total score ranging from 1-4 (representing the mean score of all 8 items). Higher scores indicate higher self-determined motivation for solitude.