The Effect of Patient Preference for Treatment Model in Internet Delivered Cognitive Behavior Therapy for Generalized Anxiety Disorder

The goal of this clinical trial is to investigate the effect of allowing patients to choose between two internet-based cognitive behavioral treatments (ICBT) for generalized anxiety disorder (GAD). The goal is also to examine psychologists' ability to predict which of the two treatments the patient will benefit most from. The main questions it aims to answer are: * Do patients who are randomized to choose their treatment improve more in their GAD symptoms compared to patients who are randomly assigned to a treatment? * Does allowing patients to choose their treatment increase treatment adherence, compared to being randomly assigned to a treatment? * Does allowing patients to choose their treatment increase treatment satisfaction and credibility, compared to being randomly assigned to a treatment? * Does allowing patients to choose their treatment increase patients' sense of agency related to the treatment process, compared to being randomly assigned to a treatment? * Do patients who receive a treatment that matches the psychologist's prediction of which treatment would fit the patient best show better treatment outcomes (primarily reduction in GAD symptoms over time, but also secondary outcomes such as satisfaction), compared to patients who receive a treatment that does not match the psychologist's prediction? Participants included in the trial will be randomized to one of two conditions: 1) read short descriptions of the two treatment programs and based on that choose the preferred treatment, 2) randomly being allocated to one of the two treatments. The two internet-based treatment programs which the patients can choose between or be randomly allocated to are: 1) Intolerance of uncertainty-based ICBT and 2) Metacognition-based ICBT. Both programs consist of 8 treatment modules and run for 10 weeks. Patients in both conditions receive continuous support by a psychologist through a built-in message function on the treatment platform. The patient will receive feed