(1) Objectives: A) To determine pilot efficacy of primary transdiagnostic protocol based on repetitive negative thinking on three person with co-occurrence anxiety and depression disorders; B) To compare efficacy of primary transdiagnostic protocol based on repetitive negative thinking with Barlow transdiagnostic protocol (2011) in symptoms reduction of patients with co-occurrence anxiety and depression disorders.
(2) Design: General plan of this study is consisted of experimental pre-test and post-test with control group and follow-up period.
(3) Setting and conduct: In the beginning, primary transdiagnostic protocol based on repetitive negative thinking was designed. Then, in order to pilot efficacy of primary protocol, it will be carried out on three patients with co-occurrence anxiety and depression disorders. After pilot study, samples will be selected then they will be randomly assigned to research groups. Assessment of the tools used in research will be performed by a trained assessor other than the researcher in three steps of before treatment, at the end of treatment, and after a 2-month follow-up. At the end, desired treatments will be individually carried out on research sample.
(4) Participants: The research sample is consisted of 45 patients with co-occurrence anxiety and depression disorders that will be selected from undergraduate students referred to counseling and psychological services center of Sharif University. They will be randomly assigned to three experimental and control group. (15 participants in experimental group 1, 15 participants in experimental group 2 and 15 peoples in control group or wait-list group).
(5) Intervention: The first intervention is consisted of 12 sessions (each session is 45 minutes in a week) of transdiagnostic therapy based on repetitive negative thinking for experimental group 1. The second intervention is consisted of 12 sessions (each session is 45 minutes in a week) of Barlow transdiagnostic protocol (2011) for experimental group 2.
(6) Main outcome measures: main outcome measures variables in this research are anxiety, depression, repetitive negative thinking, emotional dysregulation, metacognitive beliefs and experiential avoidance.