Study design and population

In this longitudinal non-randomized controlled study, the WABC group was compared with a treatment as usual group. We used a difference-in-differences approach to investigate changes in employment participation before and after implementation of WABC in comparison to the control group. A randomized controlled trial was not feasible because the referral of participants towards the WABC program or the regular employment services was controlled by the employment professionals.

From 2019 until 2020, professionals from the employment services informed persons who were enrolled in the WABC program or the regular employment services about this study. In case the client wanted to participate in the study, they were referred to the researchers. Informed consent was obtained from all participants in the study with specific consent for linking their data with information from Statistics Netherlands on employment status. Participants were followed for 12 months with three questionnaires that were administered at the start of the program, after 6 months, and at 12 months. Register data from Statistics Netherlands on employment status was used over the period 2015–2020. The Medical Ethical Committee of Erasmus MC Rotterdam declared that the Medical Research Involving Human Subjects Act does not apply to the current study (MEC-2019-0118).

Figure 1 shows the flow of participants through the phases of the study. In total, 41 persons in the WABC group and 57 persons in the control group enrolled in the study and filled out the first questionnaire. Respectively 4 (WABC) and 14 (control) persons did not provide consent for data linkage and for 2 (WABC) and 6 (control) persons the data linkage was not successful. Finally, 35 persons of the WABC group (85%) and 37 persons of the control group (65%) were included in the merge with data from Statistics Netherlands. Enrichment of the questionnaire data with register data on employment status from 2015 up to 2020 resulted in 2520 monthly observations of 35 persons in the WABC group and 2565 monthly observations of 37 persons in the control group. Information regarding mental health was solely used from the questionnaires. All 3 questionnaires were completed by 28 persons of the WABC group and 30 persons of the control group.

Fig. 1

Flow chart of participants of an interdisciplinary employment program or control group

Intervention: WABC

WABC is an interdisciplinary approach in which professionals from the mental health services collaborate with professionals from the employment services. When a client with a severe mental disorder mentions to the mental health professional that he or she would like to work (more), the mental health professional contacts the employment services for the intake procedure of WABC. The mental healthcare and employment services professionals work together on a ‘work first’ approach, to find a job that is suitable for the client. Continuity of support is provided by the mental healthcare professional from the flexible assertive community treatment (FACT) team and the professional from the employment services. The FACT team consists of professionals from mental health services, social work, nurses, etc. that are specialized in treating persons with severe mental disorders (GGZ Central 2022). Severe mental disorders include, but are not limited to: psychotic disorders, bipolar disorders, personality disorders, and addiction (Dutch Association of Pyschiatry 2021). When a job opportunity is identified, the client can start a trial period at one’s new job. During the first months at the new job, the client is supported by a job coach and the professionals of WABC according to their needs. In addition, financial support is available for the employer. On average, the program lasts for a year and participants have weekly meetings with the professionals, but this can be adjusted to the individual’s needs. This includes both the process of finding the client a job as well as the support once they start a job. However, the length and frequency of the meetings can be adjusted to the client’s needs. If the participant is performing well at their new job and their mental health is stable, the meeting frequency will slowly decrease. In case a participant needed support for a longer period, this support was provided for as long as they needed. Typical features of WABC compared to the usual employment programs of the employment services are (i) continuity of care/support after entering (or losing) paid employment, (ii) job coaching after entering paid employment, and (iii) collaboration of the employment services with mental healthcare services.

Control group: usual employment programs

The employment services support persons with social security benefits in entering paid employment. In the Dutch labor market, persons with social security benefits are required to actively look for a job. The employment services support clients in the process of searching for a suitable job by providing training to clients and by actively matching clients and employers.

Data collection

For the WABC group, questionnaires were completed through structured interviews in person (N = 11) with the researcher between April 2019 and March 2020. Because of COVID-19 restrictions, the questionnaires that followed between March 2020 and December 2020 were completed through interviews by telephone with the researcher (N = 30). For the control group, questionnaires were sent to their home address between April 2019 and December 2020 with the possibility to schedule a phone interview. Reminders were sent twice, respectively two and four weeks after sending out the questionnaire. Questionnaire data were enriched with information from Statistics Netherlands concerning participation in paid employment.

Participation in paid employment

Participation in paid employment was assessed with data on monthly employment status from registry data of Statistics Netherlands between 2015 and 2020. This information is derived from the Dutch tax registers. Paid employment was defined as having income from paid employment as the main source of income. With this information, employment history up to 5 years before entering this study was taken into account.

Health

Mental health was measured by the validated 5 item Mental Health Inventory-5 (MHI-5), which measures common mental health symptoms (e.g., anxiety, depression and psychological distress) (Berwick et al. 1991; McCabe et al. 1996). Example questions of the MHI-5 are: “During the past 4 weeks, how much of the time have you felt calm and peaceful” and “During the past 4 weeks, how much of the time have you felt so down in the dumps that nothing could cheer you up?”. A 6-point answer scale was used, ranging from: “all of the time”, “most of the time”, “a good bit of the time”, “some of the time”, “a little of the time”, to “none of the time”. A sum score was then calculated and transformed to a range from 0 to 100, with a higher score indicating a better mental health (Berwick et al. 1991). The reliability of the MHI-5 has been tested with a Cronbach’s α of 0.84 (McCabe et al. 1996). Perceived health was measured with one validated question [‘In general, would you say your health is …’] and five answer categories “very good”, “good”, “fair”, “bad”, and “very bad”, which were clustered in three groups: (very) good, fair, and (very) bad. The reliability of the SF-12 has been tested with a Cronbach’s α ranging from 0.72 to 0.89 (Jenkinson and Layte 1997; Resnick and Parker 2001; Salyers et al. 2000).

Individual characteristics

Personal information on age, sex, migration background, education, having children, and marital status were collected by the baseline questionnaire. Education was divided into three categories: low education (no education, primary education or pre-vocational training), intermediate education (vocational training), and higher education (higher secondary education and university). Marital status was used to distinguish between participants who were married and/or living with a partner from others. Migration background was divided in two categories: native Dutch (participants and parents were born in the Netherlands) and non-native Dutch (participant or at least one parent was born outside the Netherlands).

Process evaluation

During the study, 20 semi-structured interviews and one focus group interview were conducted with professionals of WABC (n = 9), participants (n = 7) and employers (n = 7) to gain insights into strengths and weaknesses of the WABC strategy and barriers and facilitators for the implementation of WABC. Interviews were conducted online through Microsoft Teams or by telephone and the length ranged between 25 and 50 min. The interviews were transcribed verbatim. Afterwards, the interviews were analyzed in NVIVO (QSR International Pty Ltd 2020).

Statistical analysis

Descriptive statistics were used to describe the WABC and control group. Logistic regression analyses were used to investigate differences in individual characteristics between the WABC and control group.

Difference-in-differences analyses were performed to investigate changes in employment participation among participants of WABC and welfare recipients receiving regular employment services (control group). First, a dichotomous variable (group) was included for the WABC (1) and control group (0). Second, a time-dependent variable was included for the time in years before the start of WABC/regular employment services (time before). An interaction term of group*time before was included in the model to test the parallel assumption referring to parallel trends in both groups before starting with WABC or regular employment services. Third, a dichotomous variable was included for the period before (0) and after (1) starting WABC or regular employment services (step change). Fourth, a time-dependent variable was included for the time in years after starting WABC or the regular employment services (time after). Interaction terms of group*step change and group*time after were included in the model to analyse differences between the WABC and control group in changes in employment participation in the year of and the years after starting with WABC or regular employment services. The difference-in-differences model was adjusted for social demographic characteristics (age, sex, education, migration background) and household characteristics (marital status, children). A random intercept was included in the model to account for dependency across multiple observations within individuals.

A generalized linear mixed-effects model was used to investigate changes in mental health among persons who participated in WABC or regular employment services. A variable for time in years from starting WABC or regular employment services up to December 2020, was included. Differences in baseline level and changes in time of mental health between those who participated in WABC or regular employment services were investigated with interaction terms of group*intercept and group*time. The model was adjusted for social demographic characteristics (age, sex, education, migration background). A random intercept was included in the model to account for dependency across multiple observations within individuals. Furthermore, this model was used to explore the differences between sex and age by stratifying for these variables. All analyses were performed using Stata 16.