Design

This research is part of a larger cluster-randomized trial [33] that was designed to evaluate the effectiveness of a training in the inquiry of traumatic events. The study was approved by the local ethics committee (‘Ethikkommission der Ärztekammer Hamburg’) and was conducted in accordance with the Declaration of Helsinki [34]. This study is not a clinical trial, i.e., a study that prospectively assigns human participants to health-related interventions to evaluate the effects on health outcomes [35], and has therefore not been registered in a clinical trial register.

Participants and setting

One hundred forty-eight health care professionals of 27 German SUD outpatient treatment centers of the federal states Hamburg and Schleswig-Holstein were included in the study. To be included, SUD centers had to offer outpatient service for clients with SUD. Health care professionals from the SUD centers were included in the study if they were providing counseling or outpatient therapy for SUD clients, i.e., if they were in direct contact with clients, and if there were willing to participate.

Out of 33 SUD counseling centers contacted, the heads of 27 SUD centers, belonging to 11 different SUD organizations, were willing to participate in the study (Fig. 1). The heads of six counseling centers chose not to participate for different reasons, e.g., the counsellors had to leave work to participate in the training, another study was already being conducted at the center, or the topic of the study was perceived as not relevant for the counselors’ working practice. One hundred forty-eight SUD professionals of the 27 centers were cluster-randomized, by SUD organizations. Out of 148 randomized SUD health care professionals, 72 were allocated to the intervention group and 76 were allocated to the control group. One hundred thirty-two professionals could be assessed at baseline, including 57 (97.2%) professionals in the intervention group and 75 (98.7%) professionals in the control group. At 6-month follow-up, 74 professionals could be assessed, including 31 (54.4%) professionals in the training group, and 43 (56.6%) professionals in the control group.

Fig. 1 Flow of participants through the trial Full size image

Intervention

The one-day ‘Learning How to Ask’ training includes eight 50-min units that cover the following topics: (1) Types and prevalence of traumatic events; (2) Effects of traumatic events on mental health; (3) Symptoms characterizing posttraumatic stress disorders; (4) Barriers to trauma inquiry; (5) Learning how to ask about traumatic events; (6) Learning how to respond to reports of traumatic events; (7) Documentation of traumatic events; and (8) Trauma-related resources available in the community. In the training, health care professionals are encouraged to reflect on their current routine practice of trauma inquiry and their barriers to inquiry. Participants learn basic knowledge about trauma and their consequences. Basic rules of asking about and responding to reports of traumatic events are discussed and practiced in role-plays.

Procedure

Thirty-three German SUD centers of the federal states Hamburg and Schleswig-Holstein were contacted and informed about the study. Health care professionals were recruited from May 2014 to August 2014, and data were assessed between September 2014 and March 2015 before the intervention, at 3-month and at 6-month follow-up.

The health care professionals in the intervention group participated in the one-day ‘Learning How to Ask’ training on the inquiry of traumatic events and adequate response strategies. The training took place at the university medical center at which the study was conducted or at the SUD center if on-site training was preferred. The trainings were conducted by one experienced psychiatrist (last author) and/or one graduated psychologist (first author) in groups ranging from 5 to 16 professionals.

To standardize the content of the training, a power-point presentation covering the full training content was constructed and used for all trainings, and standardized instructions were used for all practical exercises. A short 1.5-h refresher training was conducted 3 months later. Professionals in the control group received no training during the data assessment period of the study, but received the same intervention after the data assessment had been completed. Professionals did not receive incentives for their study participation.

Measures and primary outcomes

As no validated measure exists to assess health care professionals’ barriers to trauma inquiry, we constructed a questionnaire. Six common barriers to trauma inquiry were selected based on published research (see introduction) and discussions with SUD stakeholders: ‘Feeling uncomfortable when asking about traumatic events’, ‘Fear of offending the client when asking about traumatic events’, ‘Fear of retraumatizing the client when asking about traumatic events’, ‘Fear that client may terminate treatment when asking about traumatic events’, ‘Unsure whether authorities have to be informed when perpetrator is known’, ‘No trauma-specific treatment available in my local area’. Professionals rated their level of agreement to these statements on a four-point Likert scale (0 = strongly disagree, 1 = somewhat disagree, 2 = somewhat agree, 3 = strongly agree). The primary outcomes were change over time from baseline in the six perceived barriers to trauma inquiry.

Inter-rater reliability was estimated for the six outcomes between the three measurement points (ICC, 2-way-mixed effects model) in the professionals that received no intervention, and was rated as good according to common standards [36]: ‘Feeling uncomfortable when asking about traumatic events’: ICC = .91; ‘Fear of offending the client when asking about traumatic events’: ICC = .81; ‘Fear of retraumatizing the client when asking about traumatic events’: ICC = .90; ‘Fear that client may terminate treatment when asking about traumatic events’: ICC = .80; ‘Unsure whether authorities have to be informed when perpetrator is known’: ICC = .75; ‘No trauma-specific treatment available in my local area’: ICC = .79).

Sociodemographic characteristics and potential confounders (professionals’ age, gender, migration background [i.e., immigration into Germany from another country, or born in Germany but immigration of at least one parent into Germany], professional group, duration working in the SUD center, previous trauma training within the last 3 years and type of substance use of clients [legal substances, illegal substances, or both] were also assessed by questionnaire.

Sample size

Using a repeated-measures F test with a .05-level of significance and assuming a moderate effect size of 0.60 for self-report measures to evaluate the effect of a training [37], we estimated a sample size of n = 74 to achieve 80% power to detect a medium effect size of η2 = .059 [38]. Assuming an attrition rate of 40% at 6-month follow-up, we aimed to recruit 120 study participants.

Randomization

The participants were randomized to the intervention or a control group at the level of the SUD organizations. This randomization level was chosen because professionals often worked in more than one counseling center of a provider; so randomizing at the level of the centers would have introduced contamination. The allocation schedule for the random assignment of the SUD organizations to the intervention or control group was generated by the randomization software DatInf RandList Version 1.2. Randomization was stratified by the number of health care professionals (< 20 vs. ≥ 20 employees). Allocation ratio was 1:1. No blocking was used within each of the strata. The randomization list was stored in a password-protected data file.

Main analysis

All data provided by the participants of the study were included in the Intention-To-Treat analysis, regardless of whether they received the assigned treatment or not. The training condition was compared with the control condition on the amount of change from baseline at 3-month and 6-month follow-up. The primary outcomes were analyzed by linear mixed models (LMM), adjusted for the baseline values. All available cases for each variable were used in analysis. Missing values in the independent variables were not imputed, because there were no missing data in the independent variables used in this analysis.

The professionals and the SUD organizations were included in all final models as random effects to control for the repeated measurement or the randomization at the level of the SUD organizations, respectively. The SUD counseling centers were not included as an additional random effect in the final models, because this variable explained no additional variance of the outcomes. The fixed effects of the time point (3-month vs. 6-month) and the group (intervention vs. control) and their interaction term were included in the models to test whether the group had an effect on the outcome and whether this effect changed over time. If the group by time interaction term had no effect on the outcome, we followed the principle of parsimony and removed the interaction term from the model, as it can increase standard errors.

To control for potential confounding, variables that have been shown or are likely to be related to barriers to trauma inquiry (see introduction) were included in the LMMs: professionals’ age, gender, migration background (‘yes’ or ‘no’), professional group (‘social worker’, ‘psychologist’, ‘other profession’ or ‘trainee’), duration working in the SUD center (‘0 to <2 years’, ‘2 to <5 years’, ‘5 to <10 years’ or ‘more than 10 years’) and previous trauma training within the last 3 years (‘yes’ or ‘no’). Type of substance use of clients (‘predominantly legal substances’, ‘predominantly illegal substances’ or ‘legal and illegal substances balance each other’) was included in the analysis to control for potential confounding influences, because SUD stakeholder outlined this variable as associated with trauma inquiry (a focus group discussion on the content of the training was held prior to the start of the trial). All statistical analyses were conducted with STATA (Version 14.0, Stata Corp, College Station, Texas, USA).

Sensitivity analysis

We conducted a sensitivity analysis to test whether the imputation of missing values in the outcomes would have changed the results. In this second analysis, missing data were imputed in the outcome variable (0.1% of the outcome data was missing at baseline, 1.9% at 3-month follow-up, and 0.5% at 6-month follow-up), using multiple imputation (MICE algorithm of STATA).