Mentalizing and Epistemic Trust in Patients With Anxiety and Depression.

QUALITY ASSURANCE PLAN. The researchers will review and report the process during the trial covering participant enrolment, consent and eligibility to protect participants, including reporting of harm and completeness, accuracy and timeliness of data collection.

STANDARD OPERATING PROCEDURES. Participants will be identified from community mental health services who meet all the study eligibility criteria (listed in section Eligibility). Participants will be recruited over a period of 20 months by mental health professionals (clinical psychology residents). Community sample for validation will be recruited by social media. Participants will not receive financial reimbursement for taking part in this trial.

DATA DICTIONARY. All variables collected in this study are listed and described in an electronic case report form, with associated guidelines, to ensure consistency in all gathered data. The following data will be collected in this trial:

Sociodemographical data. Anxiety symptoms: Generalized Anxiety Disorder 7-item scale (GAD-7) Depressive symptoms: Patient Health Questionnaire-9 (PHQ-9) Epistemic Trust: Questionnaire Epistemic Trust (QET) Epistemic Trust, Mistrust and Credulity: The Epistemic Trust, Mistrust and Credulity Questionnaire (ETMCQ).

Reflective functioning: The Reflective Functioning Questionnaire (RFQ-8) Functional impact: The Work and Social Adjustment Scale (WSAS) Satisfaction with therapy: The Consumer Reports Effectiveness Score (CRES-4)

SAMPLE SIZE ASSESSMENT. The study has sensitivity to detect effect sizes that are considered clinically significant (Cohen's d =0.50) for a power of 0.8, an Alpha of 0.05 and an estimated sample of 100 participants. The calculation was performed with the GPower 3.1.9.2 program for a mean difference with a t-test for two independent groups.

For the validation of the QET, taking into account the subject-item ratio of at least 5: 1 (24 items), and considering the minimum number of recommended subjects to perform an Exploratory Factor Analysis, the minimum number of participants must be 150.Thus, estimating losses of 20%, the total number of participants estimated for the validation is n = 180 .

STATISTICS ANALYSIS PLAN. The analysis will be made following an intention-to-treat procedure. The change of means in the primary outcome variable between the two study groups will be analyzed with the Student's t-test for independent samples if the criteria for its application are met. If the criteria for its application are not met, nonparametric tests will be used. For continuous secondary variables, this test will also be used. A multivariate analysis of variance (ANCOVA) will also be considered to introduce any possible covariate that differs between the two comparison groups in the first evaluation. Potential confounding variables will include gender, age, previous level of depression and anxiety, and diagnosis. A 95% confidence level will be used for all comparisons. The R program will be used for all statistical analyses.

PLAN FOR MISSING DATA. Each researcher is responsible for ensuring that any missing data will be reported as missing in the study database. Procedures can sometimes be considered when using statistical methods that fail in the presence of any missing values, or when in the case of multiple-predictor statistical models all the data for an individual would be omitted because of a missing value in one of the predictors. For analyses involving multiple regression analysis, a multiple imputation approach will be considered and used if statistically sound, depending on the proportion and pattern of missing values.

METHODS TO ENSURE VALIDITY AND QUALITY OF DATA. Accurate and reliable data collection will be assured by verification and cross-check of the case report form (CRF) against the researcher´s records (source document verification). Source document verification will be conducted for 5% of data in subjects. Discrepancies and queries will be generated accordingly in the CRF for online resolution by the researcher at the site. In addition, the CRF data will be reviewed on an ongoing basis for medical and scientific plausibility.

Inclusion criteria

• Participants are 18 years or older.
• Participants have a diagnosis of ICD-10 F32, F33, F34, F41.1, F41.2, F43 or F43.2.
• Participants have minimal relational skills to participate in group therapy.
• Participants agree to be part of the study by giving signed written consent.

Exclusion criteria

• Participants have a diagnosis of ICD-10 F10-19, F20-29, F31, F42, F43.1, F60.
• Participants with cognitive deficits assessed during the initial interview or diagnosis of ICD-10 F70-79.
• Participants with planning or structured suicidal ideation.
• Participants with difficulties in relational skills evaluated during the initial interview.