The aims of this observational survey are to i) gather experience on how to conduct a prevalence study of mental disorders in the Norwegian setting, ii) collect data on the prevalence, risk factors and consequences of mental and substance use disorders, iii) collect data on treatment coverage for mental and substance use disorders, iv) conduct a thorough nonparticipation analysis.

The psychiatric survey was a sub-project in the fourth wave of the Trøndelag Health Study (HUNT4), conducted on HUNT4 participants aged 20 to 65 years from the geographical areas Nord-Trøndelag and the city of Trondheim. The targeted sample size was 4,000 participants, and 16,602 persons from the study population of HUNT4 participants were invited to reach this goal. The only exclusion criterion was insufficient understanding of Norwegian or English. The investigators had complete lists with postal addresses and mobile phone numbers for all eligible participants as well as information about date of birth and gender. Potential participants were sampled in repeated probability sampling draws over the course of the data-collection period, which lasted from November 2nd 2018 to September 18th 2020. Younger persons were oversampled to adjust for the expected larger nonparticipation among these age-groups. The predesignated participants were informed about the project through postal letters. A week after receipt of the letter, each received an SMS with information on how to sign up for the psychiatric interview. One SMS reminder was sent to persons who did not respond to the initial invitation. The investigators made four contact attempts to schedule the interview amongst those who registered; three by phone and one final by SMS. All participants received a $30 gift card as a token of appreciation. Computer assisted face-to-face or telephone interviews were conducted by trained and certified interviewers at local field stations. The World Health Organization (WHO) Composite International Diagnostic Interview, fifth version (CIDI 5.0) was used as instrument in the data-collection.

Inclusion Criteria:

• Sufficient understanding of Norwegian or English to conduct the interview

Exclusion Criteria:

• None

Sub-sample of participants from the fourth round of the Trøndelag Health Study (HUNT4). All residents in Trøndelag county of Norway above age 18 were invited to the HUNT4 study.

Researchers may gain access to participant data by contacting the PsykHUNT publication committee (anne.reneflot@fhi.no). Approval from the Norwegian Regional Committee for Medical and Health Research Ethics (https://helseforskning.etikkom.no) is a pre-requirement. The PsykHUNT dataset is administrated by the HUNT databank. Guidelines for access to PsykHUNT data are found at https://www.ntnu.edu/hunt/data.

June 2021 to September 2030.

Approval from the Norwegian Regional Committee for Medical and Health Research Ethics (https://helseforskning.etikkom.no). The data must be stored in secure servers which require log in and from which no data can be extracted and copied.