A naturalistic pilot study 55 randomization. This will enable us to include more participants in the experimental condition and will provide enough power for secondary analysis of effectiveness for completers. The different durations of the IMR-training—which ranged from 8 to 17 months (M = 12.7 months, SD = 2.87)—were on average somewhat longer than the 9 to 12month range mentioned in McGuire’s review, and also longer than those in three earlier RCT studies in which IMR was applied in a weekly group format (8, 9). The durations of 15 and 17 months of two groups are a particular cause for concern. For properly feasible planning of the RCT, we have therefore asked the institute to try to maximize IMR length at around 12 months. This is because if we plan the first follow-up measurement after one year in the RCT, an IMR length of longer than 1 year would mean that participants would not have completed the whole curriculum, which might be seen as a disadvantage. Conclusions The main objective of this pilot study was to assess the feasibility of conducting an RCT. Our results with regard to the recruitment of sufficient participants, to clients’ and clinicians’ satisfaction with IMR, and to the effectiveness of the program all suggest the feasibility of our primary objectives for this pilot study, which regard implementing the IMR-training program on a broader scale at Bavo Europoort. The feasibility of an RCT is also suggested by the results regarding our secondary objectives regarding the quality of implementation: to implement IMR with satisfactory fidelity, to set up a proper infrastructure for education and supervision, and to achieve an acceptable dropout percentage and a predictable program duration. If the institute is willing to follow our recommendations on recruitment, improving fidelity, training and supervision, and duration of the program, feasibility might even be greater. Generalizability A precondition for generalizability of the feasibility found in this pilot study is that other institutions have the same drive to create a comparable infrastructure for implementing and sustaining IMR, and also have comparable potential for doing so: this is because implementing six IMR groups from scratch required a considerable effort on the part of the institute. This pilot study has limitations that impair generalizability of some results. As stated above: it was only for completers—49% of all participants—that we could measure effectiveness and satisfaction. As the RCT was planned for implementation in the
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