Pre-treatment Symptom Variables

Symptom variables were collected pre-treatment and included level of depression load, rumination, and self-efficacy.

Levels of depression load at pre-treatment were measured using the MADRS-S which consists of nine items. The sum of the scores for the nine items ranges from 0 to 54 where higher scores indicate higher depression load. The online version of MADRS-S has demonstrated good psychometric properties (35).

To measure the pre-treatment level of rumination the Rumination Response Scale [RRS; (36)] was used. The RRS is a 22-item four-point Likert scale questionnaire that assesses the degree of ruminative responses to depressed mood. Each item is rated from 1 (almost never) to 4 (almost always) resulting in a total score ranging from 22 to 88, in which a higher score indicates higher levels of rumination (37). The RRS have demonstrated good internal consistency and have been validated in previous studies (38, 39).

The pre-treatment level of self- efficacy was measured using the General Perceived Self-efficacy Scale [GSE; (40)], which comprises 10 items scored 1 (Not at all true) to 4 (Exactly true). Examples of the items are “I can solve most problems if I invest the necessary effort”; or “I can remain calm when facing difficulties because I can rely on my coping abilities.” Total scores range between 10 and 40, with a higher score indicating more self-efficacy. The GSE has demonstrated good psychometric properties (41).