249 General discussion Based on the information described above, we learned the following lesson regarding the recruitment and participation of workers in a vulnerable position at the workplace. The recruitment of workers through an OHP may not be desirable, as workers, and especially those with a lower SEP, may feel less at ease to talk openly about their (health) problems with a professional and/or physician. Probably caused by unfamiliarity about their role or a lack of trust (16), which is especially the case for occupational physicians (OPs) (12). Relationships of trusts are one of the essential parts to reach and involve workers with a lower SEP (10). Therefore, it may be better to recruit workers for interventions through their supervisor. In most cases, workers have built a relationship of trust with their supervisors, due to more frequent contact and with their role of being a first point of contact in case of (health) problems. Study designs to evaluate interventions in practice In this thesis two interventions were evaluated in occupational health practice, namely the Grip on Health and ‘Mentorwijs’ intervention. The evaluation of Grip on Health consisted of a process evaluation to gain more understanding on how interventions work in real world settings (17). An existing evidence-based intervention (i.e. the Participatory Approach) was adapted and tailored to the needs and wishes of workers with a lower SEP and OHPs. Since Grip on Health was based on the evidence-based PA, an evaluation of Grip on Health in a randomized controlled trial (RCT) was deemed not needed. Therefore, a mainly qualitative process evaluation was conducted to determine how and under what conditions the intervention is feasible and applicable among both lower SEP workers and OHPs. Moreover, conducting a RCT was potentially less feasible for several reasons. Researchers argue that it is hard to obtain the required conditions for an effect evaluation, due to the complexity of interventions and the context (18). The results of chapter 4 and 5 in this thesis showed that the implementation of Grip on Health was complex in occupational health practice, and thus difficult to control for in a RCT. For instance, Grip on Health was implemented in different organizations and delivered by different OHPs among workers in different types of workplace settings. In case an RCT was conducted it would therefore have been difficult to differentiate whether intervention effects result from the intervention itself or from differences within or between organizations (18). Thus, even if an RCT shows positive results, it remains uncertain whether these results also apply to other workplace settings, and in case of negative results, it is hard to explain why positive effects are missing. Therefore, we should explore alternative research designs that provide more knowledge on how an intervention works in the complexity of work settings. For instance, participatory action research, realist evaluation and responsive evaluation are all methods that actively engage participants and other relevant stakeholders in defining changes and outcomes for evaluation (19-22). These methods offer more flexibility to align evaluations to 8
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