The MOOD trial is designed as a prospective, randomized controlled multi-arm trial with three parallel groups: an intervention group that will be screened 4-weekly for MDD for 12 months and receives a referral for MDD diagnosis and treatment after one positive test score on the PHQ-9, an intervention group who will be screened the same as the first group but receives a referral for MDD diagnosis and treatment after three consecutive positive test scores on the PHQ-9 and a control group who do not receive mobile-based screening for MDD. Randomization will be performed by the Your Research application as block randomization with a 2:1:1 allocation and stratification for age, gender and living area.

The intervention will be powered to demonstrate an effect on quality of life after 12 months with 80% power at a 5% significance threshold. It assumes that averted MDD will result in a 0.40 improvement in quality of life and that frequent screening will be effective in 40% of participants with MDD. Furthermore, the investigators conservatively assume a cumulative incidence of MDD during 12 months of 10%, based on a three times increased rate of unemployment in the intervention area and therefore three times increased risk of developing MDD. An additional adjustment for an assumed 40% spontaneously remission rate within 12 months was applied. With a correlation coefficient of 0.8, the design effect for using the baseline measurement becomes 0.36. Therefore, 714 people are required in control and combined intervention arms. Yielding a total sample size of 1,428 people (2:1:1 randomization). The intervention will be powered to demonstrate an effect on quality of life with 80% power at a 5% significance threshold. To compensate for the potential 20% differential loss of follow-up in both arms due to adverse events, the investigators aim to recruit an additional 179 participants for the control arm and 179 participants for the intervention arm (1:1 between both intervention groups). To reach the goal this study therefore need 1786 participants.

Participants will follow the individual screening procedure through the application platform Your Research. Participants will be invited to create a secured personal account, after which all participants can log in through a website on their computer/laptop or by installing the Your Research app on their tablet or mobile phone. There will be a variety of platforms provided for additional inquiries about the study process, including video calls, chat options, and phone calls.

Participants will be recruited through different online and offline strategies to encourage citizens' participation according to different cultural backgrounds. Offline recruitment includes in-person interactions with community members referred to be "key figures", posting flyers in GP offices and municipal buildings, video promotion, presentations, and by addressing people personally in public areas. Online recruitment postings will be made on websites, social media networks, and local radio stations.

Interested individuals can enroll by visiting the study website, or by initiating an application procedure through the Your Research app. If preferred, contacting the investigators through phone or email is also possible. Eligible participants will subsequently be provided with the patient information form (PIF) as well as an informed consent form. Participants who complete and return the signed consent form will be enrolled and randomized in the trial. The informed consent procedure is conducted digitally by using ValidSign. After randomization, participants will complete the baseline assessment.

Recruitment will be closely monitored to ensure that the sample size will be reached. If the sample size is attained, inclusion tactics will be discontinued. Furthermore, to ensure that questionnaire assessments are completed and that participants remain in the study, researchers will automatically send reminders via several contact channels based on the participants' preferences (email, push notifications, SMS). Participants will be compensated for their participation at the end of the study. Depending on the study arm and the number of completed questionnaires the participants can earn up to €50 in gift cards. Participants have the option to withdraw from the study at any moment during the trial. Recruitment will take place between January 2024 and December 2024.

Primary and secondary outcome measures for the MOOD study will be collected using mobile-based questionnaires. Data can be collected throughout the study and stored using encrypted digital files within password-protected folders with access limited to a restricted number of researchers. To protect confidentiality, participants will be granted a unique participant identification number upon registration. This number, as well as the associated personal information, is only available to the lead investigator and team members under their supervision. Contact information will be kept separate from any other research data gathered throughout the study. After the study is finished, all data will be safely archived for 15 years within Erasmus Medical Center. Once all outcome data has been collected, it will be exported to a statistics program. Members of the research team will examine and clean the data. All data will be kept and stored in accordance with the Personal Data Protection Act.