Study setting {9}
The study will be conducted in vocational schools in the three German federal states of Schleswig-Holstein, Bavaria and Hamburg.
Eligibility criteria {10}
All vocational students will be eligible to participate in the study if they or one of their legal guardians (if the student is under the age of 16) provide written informed consent.
Who will take informed consent? {26a}
Trial participants and if under the age of 16, their legal guardians, will be provided with sufficient verbal and written information about the study’s purpose and procedures, information on confidentiality and data protection procedures, possible advantages and disadvantages of participation, and the option to withdraw from the study at any time and without any given reason. They are informed that participation in the study is completely voluntary. Written informed consent will be obtained from all participants prior to study enrollment.
Additional consent provisions for collection and use of participant data and biological specimens {26b}
The consent includes participant’s agreement on the collected data being used and published in an anonymized form for research purposes. This trial does not involve collecting biological specimens for storage.
Interventions
Explanation for the choice of comparators {6b}
The comparator is an education as usual waitlist control group. All participants will be randomly assigned to either the app-based intervention group or the control group. The participants of the control group will continue routine activities during the (approximately) 6-week waiting period. After post-assessment, participants of the control group will receive full access to the intervention app.
Intervention description {11a}
“Meine Zeit ohne” [my time without] (MZo) is an app-based intervention that aims to encourage users to voluntary abstain from an individually relevant habitual behavior or to reduce it to a degree that is subjectively considered significant or a “challenge” for a period of two weeks. After downloading the app (downloadable for devices running on iOS 11.0 or higher /Android 6 or higher) and log-in with a password, students can set their individual challenge. For the next two weeks participants receive push notifications on a daily basis and are asked for feedback about whether they have reached their goal of the preceding day. MZo primarily targets consumption behavior (both substance related and non-substance related behavior, i.e., digital/ screen based media related behavior such as gaming and/ or social media use).
Criteria for discontinuing or modifying allocated interventions {11b}
Participants in the intervention group can discontinue the use of the intervention app at any time by deleting the app from their mobile device. The intervention, i.e. the use of the app does not require any contact to the study team.
Strategies to improve adherence to interventions {11c}
The implementation of the MZo-Challenge is entirely app-based. The effort required to use the app can be considered minimal. Adherence to the intervention is facilitated by an easy access procedure (log-in and user authentication is only required once after the download of the app) and daily push notifications. The app provides the opportunity to choose individual behavior change goals from a broad spectrum including an undefined goal category which can be specified by the individual user.
Relevant concomitant care permitted or prohibited during the trial {11d}
Participation in the current trial has no impact on possible concomitant care during the time of the trial.
Provisions for post-trial care {30}
All participating schools are provided with contact information of the study sites and can access evidence-based information material on substance use and substance use prevention via the project website.
Outcomes {12}
Primary outcomes
Outcome measures at each time point are shown in Figure 2. Primary outcomes are self-reported use of alcohol, nicotine (cigarettes and/ or electronic cigarettes), digital media (gaming and social media) in the past month. Measures for alcohol use are based on [22] and include frequency of drinking (1 = “never” to 5 = “four times a week or more”), quantity of alcoholic drinks on a typical drinking day (1 = “1 or 2 alcoholic drinks” to 5 = “10 or more alcoholic drinks”) and frequency of binge drinking (more than 6 alcoholic drinks on one occasion; 0 = “never” to 4 = “daily or almost daily”). Nicotine use is assessed based on students’ reports on the number of days using cigarettes and/ or electronic cigarettes and their quantity per day. Problematic Internet gaming is assessed using the Internet Gaming Disorder Scale-Short-Form (IGDS-SF; [23]), German version ([24]; 9-items: e.g., “Have you continued your gaming activity despite knowing it was causing problems between you and other people?”; 1 = “never” to 5 = “very often”). Problematic social media use was assessed using an adapted version of the brief version of the Bergen Facebook Addiction Scale (BFAS; [25]; German version: [26]). The scale consists of 6-items (e.g., “Felt an urge to use social media more and more”; 1 = “very rarely” to 5 = “very often”).
Secondary outcomes
A number of individual-level secondary outcome measures were selected based on their health-related relevance and associability with the conceptual intervention approach. These outcomes are:
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Problematic Cannabis Use (SDS, Severity of Dependence Scale, 5 items [27]; German version: [28]).
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Problematic Gambling (BBGS, Brief Biosocial Gambling Screen, 3 items [29])
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Psychological Stress (DASS-21, Depression Anxiety Stress Scales 21, subscale stress, 7 items [30]; German version: [31])
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Impulsivity and Sensation Seeking (SURPS, Substance Use Risk Profile Scale, subscales impulsivity and sensation seeking, 2 items each [32])
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Mindfulness Skills (CAMM, Child and Adolescent Mindfulness Measure, 10 items [33])
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Physical activity (past month frequency of physical activity/ sports, single item, self-constructed)
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Positive mental Health (PMH, Positive Mental Health-scale, 9 items [34])
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Life satisfaction (L1, General Life Satisfaction Short Scale, single item [35], German version [36])
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General Self-efficacy (ASKU, Short Scale for Measuring General Self-efficacy Beliefs, 3 items [37])
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Readiness and confidence to quit or reduce use of alcohol, nicotine, cannabis, gaming, social media, and gambling (readiness/ confidence ruler (10 = ”not at all ready/ difficult to change” to 100 = “very ready/ difficult to change”) assessing readiness and confidence in quitting or reducing each behavioral outcome; based on [38])
For a list of included secondary outcomes see Figure 2. Additionally, we assess socio-demographic data (age, gender, migration background, socio-economic status), progress of vocational education, educational sector and frequency of in-school education.
Participant timeline {13}
In Fig. 1, trial procedures from enrollment to the end of the trial are illustrated.
Sample size {14}
The sample size is calculated to detect a minimum relative difference of 20% between both groups at post-assessment. This effect was based on previous studies on the effectiveness of substance use prevention programs [11, 39] and takes a clustered-data structure and an intra-class correlation (ICC) of 0.032 as well as a drop-out rate of 30% on student level into account (based on [15]). The required sample size for 80% power to detect between-group differences at the 0.05 level is 4,500 students (2,250 students per condition) from 225 classes.
Recruitment {15}
The three study sites cooperate with local school supervisory authorities, which support the project and allow recruitment of a convenience sample of vocational schools. Class teachers and other school staff (such as school social workers) at those schools are informed about the study in teacher conferences. This information includes access to the project website which features explanation videos about the MZo-app and the implementation of the study. Teachers will be provided a login-code to test the MZo-app prior to implementation in their class. If teachers decide to participate in the study, two appointments for data collection and for the introduction of the intervention will be scheduled. Consent to participate in the study on student level has to be provided prior to baseline assessment.
Assignment of interventions: allocation
Sequence generation {16a}
Randomization will be performed at class level. The randomization sequence has been created [40] using the program „Randomization in Treatment Arms” (https://www.evidat.com/rita). Classes of vocational schools will be stratified by class characteristics and paired into dyads of similar classes. The first member of a dyad will have a 50% chance to be assigned to the intervention group, the remaining class will automatically be assigned to the other trial arm.
Concealment mechanism {16b}
In the temporal order of study inclusion, allocation of classes will be made according to the randomization plan to either the MZo-intervention or the control group. Participants, teachers, and schools will have no influence on the allocation process and assignment of classes to either group but they will not be blind to randomization.
Implementation {16c}
Random allocation of classes within schools to either the MZo-intervention or the control group using the randomization plan takes place at each study site under the responsibility of the local study team. All students who give their written consent (electronically) to participate in the study, will be enrolled. Unique identifiers are generated using an ID-generator software and will provide access to the electronic assessment portal. The flow diagram of the study design is depicted in Fig. 1.
Assignment of interventions: Blinding
Who will be blinded {17a}
All participants, teachers and schools are blinded to the randomization and allocation process. However, they will not be blind to the MZo-intervention, as participants of the control group will be informed that they will receive access to the MZo-app after post-assessment.
Procedure for unblinding if needed {17b}
There is no need for unblinding.
Data collection and management
Plans for assessment and collection of outcomes {18a}
Data will be collected class-wise in schools. The baseline assessments will take place directly before the intervention, the post assessments at least 30 days after the end of the intervention. All measures are assessed via the online system “SoSci Survey”, program version 3.2.12 (15.02.2021). All collected data is entered using participant’s personal smartphones. If individual smartphones are unavailable or not functioning due to technical problems the study teams will provide tablets to ensure data collection. To guarantee a smooth online data assessment, the study teams will also provide a portable LTE-router for a stable internet connection in the classroom if necessary. As for the MZo-app and the online assessment portal, compatibility with current Android and iOS devices is given.
Plans to promote participant retention and complete follow-up {18b}
According to their allocation, study participants will complete the online questionnaires in class. Unique identifiers are distributed by the study team and can be used to access the questionnaire for pre- and post-assessments. The same identifier can also be used to log-in to the MZo-app. To maintain high retention rates between pre- and post-assessments, participants are encouraged to take a smartphone picture of their unique identifier. To maximize data completeness, vocational students who are absent from school at the day(s) of the assessment will be contacted in a coordinated approach by their teachers.
Data management {19}
Online assessment data will automatically be transferred to a local server at the study site in Kiel (SH), minimizing errors of data entry. All participant data is handled in accordance with the General Data Protection Regulation (GDPR). All data will be maintained confidentially before, during, and after the trial and is stored securely at the study site in Kiel with access only by dedicated study team members.
Confidentiality {27}
All data is collected using 6-digit unique identifiers to access the online questionnaires. The first two digits of this code identify the specific school, the next two digits identify a particular class. The last two digits that identify an individual participant are randomly distributed. Single individuals cannot be identified.
Plans for collection, laboratory evaluation and storage of biological specimens for genetic or molecular analysis in this trial/future use {33}
No biological specimens will be collected.
Statistical methods
Statistical methods for primary and secondary outcomes {20a}
Analyses will account for clustering of individuals in school classes and will be reported following CONSORT standards. Trial variables will be analyzed by intervention arm, into which participants were randomly assigned. Continuous outcomes will be reported for each trial arm using means and standard deviations and binary outcomes will be reported for each trial arm using numbers and percentages. The main intervention effects will be tested by means of logistic or linear multi-level/ random effects regression models with the levels “classes” and “individuals”, whereby group and time variables as well as the interaction term group x time are used. Primary between-group analyses will be adjusted for baseline scores of the outcome variable, relevant covariates (baseline prognostic factors that are theoretically associated with outcomes, including, but not limited to age, gender, and migration background as well as the personality traits sensation seeking and impulsiveness) and those variables used to stratify randomization.
Interim analyses {21b}
No interim analysis will be performed.
Methods for additional analyses (e.g. subgroup analyses) {20b}
For sensitivity analysis unadjusted and complete case (without imputation of missing data) analyses will additionally be carried out for primary and secondary outcomes. Potential moderators, such as individual differences in sociodemographic factors (age, sex, etc.) or vocational school-level factors (i.e., vocational sector etc.), and potential mediators (mechanisms of action) such as self-efficacy or abstinence/ reduction related control beliefs will be explored in interaction analyses.
Methods in analysis to handle protocol non-adherence and any statistical methods to handle missing data {20c}
Primary analyses will be based on the intention-to-treat population, thus including data from all participants who provide baseline data within a school class that was previously randomly assigned to one of the two trial conditions. Multiple imputation methods will be used to estimate missing data.
Plans to give access to the full protocol, participant level-data and statistical code {31c}
Anonymized study data and statistical codes will be made available on request given that data protection according to GDPR and ethics according to ethical approval is ensured.
Oversight and monitoring
Composition of the coordinating centre and trial steering committee {5d}
The coordinating centre is the primary sponsor of this trial and responsible for study supervision. The coordinating investigators at the three study sites form a steering committee for the study. They meet regularly and are responsible to critically review the study design, the study protocol, the data management, and all study-related documents. The coordinating investigators provide oversight on the trial and support the study team members who conduct and provide day to day organisational support for the trial at each site. Furthermore, the coordinating investigators are responsible for the trial registration, revisions of the study protocol and application/amendments to the ethics committee, and scheduling of regular team meetings. All involved investigators and team members ensure compliance with the study protocol.
Composition of the data monitoring committee, its role and reporting structure {21a}
Not applicable, this trial is not monitored.
Adverse event reporting and harms {22}
Information on the occurrence of adverse events will be documented. Adverse events related to the assessment or use of the MZo-app during the 2-week intervention period will be recorded by the coordinating investigator.
Frequency and plans for auditing trial conduct {23}
Not applicable, there will be no external auditing during the trial.
Plans for communicating important protocol amendments to relevant parties (e.g. trial participants, ethical committees) {25}
All protocol deviations or modifications will be documented; all substantial protocol amendments will be communicated to the ethics committee of the Center for Psychosocial Medicine at the University Medical Center Hamburg-Eppendorf, the responsible school authorities at each study site (Center for Education Monitoring and Quality Development at schools in Hamburg, IfBQ; the Center for Prevention at the Institute for Quality Development at Schools in Schleswig-Holstein, IQ.SH; and the Bavarian State Ministry for Education and Cultural Affairs) and the German clinical trial register, DRKS (DRKS00023788).
Dissemination plans {31a}
The study results will be presented at conferences and symposia and will be submitted for publication in relevant journals.