The goal of this multiple baseline case series study is to test Imagery Rescripting in depression. The main question[s] it aims to answer are:

• does Imagery Rescripting lead to a reduction of depression and of believability of negative beliefs held by the participants?
• does Imagery Rescripting also leads to reductions in worrying and brooding?
• Participants will wait for 6-10 weeks (to assess time effects without treatment), followed by 5 weekly preparation sessions, 8-12 weekly Imagery Rescripting sessions, and 5 weeks post-treatment.
• Participants will rate the believability of 3-5 core dysfunctional beliefs related to their depression as well as 2 items assessing depression severity on a weekly basis. In addition, they will fill out more extensive questionnaires on depression, worry and brooding before each phase, as well as at 5 weeks post-treatment, and 6 and 12 months follow-up.

In a multiple baseline case series study the effectiveness of Imagery Rescripting (ImRs) as a treatment for depression will be tested. 10 patients with a major depressive disorder (MDD) or a persistent depressive disorder (PDD) will be randomized to different waitlist lengths (6-10 weeks), after which they will enter a 5-session preparation phase (5 weeks), followed by 12 weekly sessions of ImRs. After this treatment follow-up assessments take place at 5 weeks, 6 and 12 months. Primary outcomes are (1) depression severity weekly assessed with the Patient Health Questionnaire (PHQ-2) and (2) idiosyncratic core beliefs assessed with visual analogue scales. The hypothesis is that primary outcomes reduce more during treatment than during wait or preparation and remain stable or further improve post-treatment. Similarly, for secondary outcomes (depression severity assessed with the Beck Depression Inventory II (BDI-II); brooding (dysfunctional type of rumination) assessed with the Ruminative Response Scale (RRS) Brooding subscale; and worrying assessed with the Penn State Worry Questionnaire (PSWQ)) we expect the largest improvement to take place from pre- to post treatment, with little change taking place during baseline and preparation, and during/after post-treatment.

Results will be analyzed by multilevel analysis, pooling the effects of the individual cases. Lastly, participants will be interviewed 5 weeks post treatment about their experiences with treatment.

Inclusion Criteria:

• Primary diagnosis of MDD as assessed with the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) (SCID-5)
• Total score of 20* or above on the BDI-II (cut-off score for moderate depression) (Beck et al., 1996). (*Based on previous research by Brewin et al. (2009) & Yuen-tin (2017) demonstrating averages of BDI-II: 34-35, in their population.)
• Age 18-65
• Dutch or English as a first language (or estimated as sufficient to receive treatment in either of these languages without interpreter)
• Willingness to participate in the study (signed informed consent)

Exclusion Criteria:

• DSM-5 Bipolar disorder, type 1 (current or past); if there has been no manic episode the last year patients will be included
• Psychotic disorders (though psychotic features alongside depression will be allowed)
• Organic brain disease
• Intelligence Quotient (IQ) < 80
• High risk of self-harm or suicide
• Current substance abuse severe level
• Start of new medication within 2 months before beginning the study (medication used for longer periods can be continued; patients are requested to keep medication stable during the course of the study)
• Having received ImRs (either as a stand-alone or embedded in a greater treatment such as cognitive behavior therapy (CBT) or schema therapy) within the last year
• No other evidence-based treatment of MDD is allowed during the study.
• Not able to plan enough time for weekly therapy sessions (45-60 minutes); weekly measurements (estimate of 5 minutes) and other measurements (estimate of 20 minutes); and the qualitative post-treatment interview (estimate of 60 minutes) during the study period.

because of privacy regulations individual patient data cannot be shared, unless the European Union (EU) regulations on data protection are guaranteed.

The investigator will not have access to assignment of participants to waitlist length and the data until data collection is complete.