Even though internet-based interventions have been used in treatment of forensic psychiatric outpatients for over ten years, no robust research into their effectiveness has taken place. Multiple potential benefits and barriers have been observed in clinical practice, such as the possibility to increase a patient's treatment readiness, self-efficacy and thus reduce undesired behaviour such as reactive aggression. However, therapists indicate that these interventions do not seem to work for all forensic psychiatric patients, and that uptake is generally quite low. There is an urgent need to evaluate if and how these internet-based interventions are of added value for treatment of forensic psychiatric outpatients.

The main goal of this study is to investigate whether the addition of the existing internet-based intervention 'Aggression' to treatment as usual of forensic psychiatric outpatients leads to better treatment outcomes than treatment as usual that is delivered solely in-person.

This study uses a multicentre mixed methods randomized controlled trial (RCT) design, with four participating Dutch forensic psychiatric outpatient care organizations. Patients are included if they receive outpatient treatment for aggression regulation problems and will be randomized into an experimental condition, in which the internet-based intervention is added to treatment as usual (TAU), or a control condition, with only TAU. Participants are assessed four times: at baseline (T0), halfway during the 10-week intervention (T1), after completing the intervention (T2), and after three months (T3). Primary outcome measures are regulatory emotional self-efficacy, treatment readiness, and aggression, assessed via validated self-report questionnaires. Secondary outcome measures are the number of in-person treatment sessions during the data collection, and dynamic risk factors. Adherence to and engagement will be studied as potential predictors for effectiveness via respectively log data and a self-report questionnaire. Perceived benefits, barriers and points of improvement will be identified via qualitative interviews with participating patients and therapists.

This will be the first experimental study to investigate an internet-based intervention in a forensic psychiatric outpatient sample. By using a mixed-methods design and by adding adherence and engagement as potential predictors, this study can not only answer questions about if, but also why and for whom this intervention works. Consequently, this study will answer an important question from clinical practice: are these types of interventions - which have been used in practice for over ten years - actually of added value for treatment?

Rationale: While internet-based interventions have been used for over ten years in Dutch forensic psychiatric outpatient care, no thorough evaluation study has been conducted yet. Studies on internet-based interventions in other mental healthcare sectors show promising results: they can increase the quality and efficiency of care. However, it is not clear if, why and for whom these interventions work in forensic mental healthcare. It is especially important to study whether these interventions are of added value for this complex patient population, known for its low treatment motivation, co-morbidity and low literacy levels.

Objective: The primary objective of this study is to investigate whether the addition of the internet-based intervention 'Aggression' to forensic psychiatric outpatient treatment as usual (TAU) results in better treatment outcomes in terms of self-reported regulatory emotional self-efficacy, treatment readiness, and aggression. Additionally, it is investigated whether the experimental group requires fewer treatment sessions and improves more on dynamic risk factors. Furthermore, to gain more insight into for whom these interventions work, it is investigated whether engagement with the internet-based intervention predicts adherence and effectiveness. Finally, this study aims to explore reasons for the (in)effectiveness of the intervention according to patients and therapists.

Study design: To investigate if the use of internet-based interventions is of added value for treatment of forensic psychiatric outpatients, a multicenter, non-blinded, parallel groups, randomized controlled trial design is used. Patients fill out three short self-report questionnaires four times: at baseline, mid-treatment (+6 weeks), post-treatment (+14 weeks) and at follow-up (+26 weeks). Semi-structured interviews with a randomly selected sample of 20 patients from the experimental condition and with all participating therapists are conducted to explain the results of the RCT.

Study population: The target group of this study consists of forensic psychiatric outpatients, treated in four Dutch organizations for aggression regulation problems.

Intervention (if applicable): This study investigates the existing internet-based intervention Aggression, which was introduced in forensic mental healthcare over ten years ago. However, as is the case with other internet-based interventions, uptake in practice remains relatively low. 'Aggression' is used as an addition to treatment as usual, and thus does not replace any part of treatment in this study. The intervention is earlier developed by the CE-certified company Minddistrict. The last couple of months the intervention has been cosmetically adjusted in close cooperation with therapists, patients and other stakeholders so that it fits the current design and lay-out of Minddistrict. The goals of this intervention are to (1) increasing the motivation to change, (2) acquiring skills for dealing with conflict, and (3) breaking the cycle of aggression by providing knowledge on situational, emotional, cognitive and physical triggers. It contains ten lessons, each containing written texts, videos and audio files, and short written assignments on which the therapist can give feedback.

Main study parameters/endpoints: All participants fill out three validated, short self-report questionnaires on self-efficacy, treatment readiness and aggression at four points during the study. Participants in the experimental conditions also fill out an engagement questionnaire during the use of the intervention. Dynamic risk factors are assessed via a risk assessment instrument that is already used as a standard part of treatment according to Dutch guidelines and the number of treatment sessions are retrieved from existing systems. The patient and therapist perspective is take in into account by means of semi-structured interviews.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Since participants only have to fill out short questionnaires, participating in this study is not viewed as a major burden. Furthermore, interventions of Minddistrict have been used for over ten years in mental healthcare, during which no risks or adverse events have been observed. Because not all forensic psychiatric patients receive internet-based interventions as part of their standard care and because these interventions are not yet evaluated and are thus not evidence-based, participants in the control condition are not deprived of effective treatment. During the entire study, experienced therapists monitor the patient's progress. Finally, multiple precautions are taken to ensure that patients are aware that the decision to participate does not have any effect on their treatment progress. Consequently, the burdens and risks associated with this study are low or even non-existent.

Inclusion criteria

In order to be eligible to participate in this study, a subject must meet all of the following criteria:

1. The patient is 18 years or older
2. The patient is treated at an outpatient clinic
3. The patient receives one-on-one treatment
4. During the intake, improvement of aggression regulation has been selected as one of the treatment objectives
5. The patient indicates that they are able to read and write simple texts
6. The therapist responsible for treatment of the patient indicates that participating will not result in any harm for the patient
7. The patient voluntarily consents to participation

Exclusion criteria

A potential subject who meets any of the following criteria will be excluded from participation in this study:

1. The patient has a current psychosis
2. The patient resides in any type of psychiatric inpatient clinic - this can be a forensic, but also another type of clinic
3. The patient receives group treatment focused on aggression regulation (specifically: AR [aggressieregulatie] op maat)
4. The patient is analphabetic, i.e. being unable to read and write
5. The responsible therapists identifies any other valid reason for exclusion

As can be seen in the in- and exclusion criteria, the responsible therapist is actively involved in determining whether participating in the study is safe and possible for the patient. This will first be discussed during the MDO. If, after several treatment sessions, the therapist identifies any reasons for exclusion, this will be communicated to the researcher and the patient will not be invited to participate.

Because an internet-based intervention is used, patients, therapists and researchers cannot be blinded to the condition to which the participant is allocated.