Effects of IMR: a randomized controlled trial 129 Although our positive results regarding the client version of the IMR scale are consistent with the results of three RCTs on IMR (22, 23, 28), they differ from those of three other RCTs (21, 24–27). Moreover, our negative results regarding the clinician version of the IMR scale are consistent with those of a previous RCT (25, 27); however, they differ from the results of four previous RCTs reporting positive outcomes (21–23, 28, 29). Our positive findings regarding personal recovery differ from those of three previous RCTs (23–25, 27). This inconsistency in results may be attributed at least in part to differing completion rates between the investigations. We thereby suggest that the differing attendance rates within IMR may have affected the findings of this and other RCTs with respect to IMR outcomes. A previous RCT that reported no statistically significant effects was conducted among a cohort with an IMR attendance of only 28% (24). Two of three RCTs with IMR completion rates of ≥50% (including our study) reported positive effects (22), while the third RCT reported null results (25–27). Two RCTs with completion rates of 100% reported positive effects on psychiatric symptoms as well as on both IMR scales (23, 28). Additionally, Levitt et al. found that, with respect to the intentionto-treat analysis, the effect size for completers increased from 0.36 to 0.75 and from 0.39 to 0.59 on the client and clinician versions of the IMR scale, respectively (22). This is consistent with our findings, wherein effect sizes on both IMR scales substantially increased in the completer subgroup. A minimum threshold of exposure to IMR could be required for treatment effects to occur (24). Therefore, in addition to the percentage of participants exposed to ≥50% of the scheduled sessions, the total number of sessions attended is also relevant in evaluating treatment efficacy. In the current study, the mean attendance for the IMR group was 23.57 sessions (SD = 21.09), with completers attending an average of 42.40 sessions (SD = 12.53). A Danish RCT (25–27) that did not observe any effects had an average attendance of 16.4 sessions; moreover, completers (defined as participants exposed to >10 sessions) had only attended an average of 26.1 sessions. Therefore, the results of the two negative trials on IMR (24–27) could be partly attributed to their respective low completion rates. The importance of a higher completion rate with respect to the efficacy of IMR suggests the relevance of increasing the motivation to continue IMR among patients. In addition to reminders and phone calls, IMR trainers should employ promote the efficient use of available places at our study sites, the current study had rolling admission into IMR groups; however, peer support—and thus participation—may be promoted if groups have a closed enrollment format (24). At one site in our study, IMR groups had lunch together at each meeting to promote
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