Pragmatic randomized controlled trial (expected N = 80) of cognitive-behavioral therapy (CBT) to contrast two psychotherapeutic implementation strategies (State-of-the-Art welcome phase vs. prolonged focus on sudden changes). Blinded allocation of implementation strategy for patients; open label for therapists (no blinding possible), randomized allocation for patients, therapist allocation via ABAB-design (crossed-therapist design). Post treatment self-reported outcome will be measured based on a latent outcome factor (i. e. "outcome composite").

State of research. The proposed trial has a common theme, i.e., the understanding of the enduring efficacy of psychological treatments in individuals who suffer from general anxiety disorder (GAD). There is meta-analytic evidence that bona fide psychotherapy is an effective treatment for GAD, but also for individuals that suffers from anxiety and depression. Nonetheless, in spite of the empirical evidence of the overall efficacy, there is a lack of randomized controlled studies that systematically investigate the therapists' variability (i. e. therapist effects) within the very same treatment protocol. The development of study designs to investigate potential health professional effects along treatment effects is a general claim for human interventions. This protocol includes one of the very first process-outcome trials in GAD that systematically examine theory-based patients' and therapists' characteristics simultaneously using longitudinal multilevel methodology.

Along with investigating therapist and patient characteristics, two methods for timing the check-in phase at the beginning of each session will be compared by keeping constant the standardized treatment manual for patients with GAD: (a) prolonged focus on subtle changes check-in condition lasting from 7 to 20 minutes and (b) a state of the art (SOA) check-in phase lasting from 5 to 10 minutes. To address the nested data structure, therapists will be allocated by a single-subject ABAB-design. A total of 80 patients (40 participants in each of the two conditions) with a primary GAD diagnosis will be treated by 20 advanced cognitive-behavioral therapy trainees at the psychotherapy outpatient clinic in the department of psychology at the university of Zürich.

Relevance. (a) Study population. GAD is a neglected disorder in the Swiss mental health system. GAD is associated with personal suffering, a reduced quality of life, and high economic costs. (b) Design development. Systematic integration of potential therapist effects is a neglected aspect in many areas of evidence-based human interventions (inside but also outside of psychological interventions). (c) Treatment development. Evidence-based treatments are usually far from being fully efficacious. There is a debate about innovative research agendas and how to foster the efficacy of such treatments. (d) Experimental process-outcome research. There is a need for future research to investigate theory-based therapist effects and in-session timing within rigorous experimental process-outcome research designs to better understand the factors involved in therapeutic change (e.g. http://www.nature.com/news/therapy-deficit-1.11477).

Inclusion Criteria:

1. fulfill the diagnostic criteria for GAD based on the structured interview for DSM,
2. are 18 years of age or older,
3. Mastery of German language
4. are seeking out a cognitive-behavioral therapy (CBT) for GAD at the outpatient clinic (Attenhoferstrasse 9) of the Institute for Psychology of the University of Zürich
5. Informed consent as documented by signature

Exclusion Criteria:

1. Acute Suicidal Ideation (BDI Suicide item > 1 or suicidal ideation in the telephone interview)
2. Currently taking a psychotic or bipolar disorder medication, or
3. Currently receiving treatment from a professional psychotherapist/psychiatrist.