Self-report questionnaire to assess subjective stress experience; 10 items; each item is rated on a 5-point scale from 0(never) to 4(very often); total scores range between 0 and 40 (higher scores indicate more subjective stress).

The German version of the RESE is a 10-item instrument measuring self-efficacy for emotion regulation. Items are scored on a Likert Scale ranging from 1 (not well at all) to 5 (very well). Higher scores indicate better regulatory emotional self-efficacy.

Self-report questionnaire to assess state and trait anxiety and depression; 40 (20 state scale; 20 trait scale) items; each item is rated on a 4-point scale from 1(not at all) to 4(very much); total scores per scale range between 20 and 80 (higher scores indicate more anxiety)

Because we felt that the existing emotion regulation scales used in this study did not capture the some of the specific skills that the emotional writing intervention targets, we created a set of five specific items about allowing, accepting, experiencing and managing negative emotions. Items are scored on a Likert Scale ranging from 1 (do not agree at all) to 5 (agree completely). Higher scores indicate better emotion regulation abilities.

Treatment expectations are measured via the generic rating scale for previous treatment experiences, treatment expectations, and treatment effects (GEEE), subscale for previous treatment experiences and subscale for treatment expectations. Answers are provided on a numeric rating scale ranging from 0 to 10 (each item has specific anchors with lower anchors always indicating no expected effects)

The items used by Kushner and Sher (1989), to assess perceived barriers were translated to German and modified to state "I am uncertain" instead of "I am anxious". The scale consists of 3 subscales: therapist responsiveness (5 items), image concerns (4 items), coercion concerns (4 items). Answers are provided on a 5-point scale ranging from 1 (not at all) to 5 (completely) with high scores indicating greater uncertainty. Five items to reflect specific uncertainties (financial concerns, time restrictions, therapist relatability, the therapeutic process, personal ability to complete therapy), that were not covered by the original article, were added. Answers are provided on a 5-point scale ranging from 1 (do not agree) to 5 (agree) with high scores indicating greater uncertainty.

Credibility of and personal reactions to psychotherapy are measured via a self-translated German version of the Credibility & Personal Reaction Scale. This scale also measures intentions to seek therapy.

Credibility scale: 7 items, answers are provided on a 7-point Likert scale from 1 (not at all) to 7 (extremely).

Personal Reactions to the Rationales (PRR): 5 items, answers are provided on a 7-point Likert scale from 1 (not at all) to 7 (extremely).

The total score of the credibility scale ranges from 7 to 49 with higher scores indicating higher credibility ratings, the total PRR score ranges from 5 to 35 with higher scores indicating more positive reactions and higher credibility.

Single-Category Implicit Associations Test (SC-IAT), measuring implicit associations with psychotherapy. It is a reaction-time task facing the target dimension 'psychotherapy' and the evaluative dimensions 'effective' and 'ineffective'. The strength of the association (D-score) between the target dimension and the evaluative dimension is calculated based on the reaction times. Shorter reaction times indicate a greater associative strength.

German version of the Self-Stigma of Depressions Scale (SSDS), 16 items measuring anticipated self-stigma for the hypothetical case that one would be suffering from depression. The SSDS consists of 3 subscales: self-blame, help-seeking inhibition, social inadequacy Answers on all items are given on a 5-point Likert-scale ranging from 1 (completely disagree) to 5 (completely agree); higher scores indicate higher self-stigma.

Part A (6 items) of the Depressive Expectations Scale (DES). Items are scored on a Likert Scale ranging from 1 (do not agree) to 5 (agree). Higher scores indicate stronger negative expectations about dealing with negative emotions.

The German 4-item scale Internale-Externale-Kontrollüberzeugungen-4 (IE-4) to assess locus of control.

The IE-4 scale consists of 2 subscales: internal (2 items) and external locus of control (2 items). The 4 items are answered using a 5-point Likert-scale ranging from 1 (strongly disagree) to 5 (strongly agree). The subscale scores are averaged into one score per subscale. The mean subscale values range between 1 and 5 with higher scores indicating higher internal or external locus of control.

Empathy via the German version of the Interpersonal Reactivity Index (IRI), a 16-item scale. Answers are provided on a 5-point rating scale ranging from 1 (never) to 5 (always). Empathy is divided into one cognitive and three emotional components: perspective taking (PT; item 4,10,14,16), fantasy scale (FS; item 2,7,12,15), empathic concern (EC; 1,5,9,11) and personal distress (PD; 3,6,8,13); the general score is determined by the sum value of the individual scales EC, PT and FS (empathy=EC+PT+FS), whereby a higher score indicates higher empathy.

The CERQ-short is an 18-item instrument measuring the habitual use of adaptive and maladaptive cognitive emotion regulation styles (self-blame, rumination, acceptance, positive refocusing, refocus on planning, positive reappraisal, putting into perspective, catastrophizing, other-blame) with 2 items per subscale. Items are scored on a Likert Scale ranging from 1 (almost never) to 5 (almost always). Higher scores indicate more frequent use of a cognitive emotion regulation style.

Public Stigma of depression are measured via the German translation of the Depression Stigma Scale (DSS), using the Perceived Stigma subscale: 9 items, measuring perceived public stigma of depression. Answers are provided on a 5-point Likert-scale ranging from 0 (completely disagree) to 4 (completely agree); total scores range from 0 to 36 with higher scores indicating greater perceived stigma.

Prior experiences with psychotherapy are measured via the generic rating scale for previous treatment experiences, treatment expectations, and treatment effects (GEEE), subscale for previous treatment experiences. Answers are provided on a numeric rating scale ranging from 0 to 10 (each item has specific anchors with lower anchors always indicating no expected effects)

Four items to assess tendencies to discredit the information viewed in the intervention videos.

We created three items relating to dealing with emotions before, after and during the emotional writing session. The three items assess: mood in the past 24 hours (item scored on a 10-point Likert Scale; higher scores indicate better mood), ability to cope with emotions in the past 24 hours (item scored on a 10-point Likert Scale; higher scores indicate more ability to cope with emotions), adherence to the emotional writing session (item scored on a 10-point Likert Scale; higher scores indicate more adherence). A forth item was taken from the Depressive Expectations Scale (DES) to assess the expectation about the ability to cope with emotions in the coming 24 hours (item scored on a Likert Scale ranging from 1 (do not agree) to 5 (agree). Higher scores indicate stronger negative expectations about coping with negative emotions in the next 24 hours)

Current treatment effects are measured via the current treatment effects subscale of the generic rating scale for previous treatment experiences, treatment expectations, and treatment effects (GEEE). Answers are provided on a numeric rating scale ranging from 0 to 10 (each item has specific anchors with lower anchors always indicating no expected effects)

Participant perceptions of warmth and competence of actors shown in the videos are measured via the Warmth and Credibility Screener - German translation: 12 items assessing perceived warmth (6 items) and competence (6 items) on a 5-point Likert scale ranging from 1 (not at all) to 5 (completely) with high scores indicating greater ratings of warmth and competence.