Strengths and Limitations
NSSI
This study had several strengths. These include the use of TAU as the control condition, the use of weekly measures of NSSI, inclusion of both self-reported and clinician-administered assessments, integrity of the masked assessments, and the sexual orientation diversity of the sample.The study also has limitations. IERITA was delivered adjunctive to TAU and compared with TAU only. Although this type of augmentation design holds value in the early stages of treatment development, the lack of equipoise between conditions precludes any conclusions regarding the specific effects of IERITA or mechanistic claims of the intervention. Also, not receiving IERITA could constitute a nocebo condition. Furthermore, although our mediation analysis included a sensitivity analysis to assess the impact of unobserved pretreatment confounders, potential posttreatment confounding (including reverse causality) was not addressed. Future studies should include an active internet-delivered control condition matched on level of activity and attention from therapist and include additional mediators (eg, self-compassion, self-acceptance, other measures of emotion regulation, therapeutic alliance) and analysis (eg, cross-lagged models) to test whether the mediator temporally precedes the outcome. Additionally, data cannot speak to whether participants’ ongoing psychopharmacological treatment was appropriately targeted and dosed. However, given that the onset, type, and frequency of counselling and psychopharmacological treatment were equivalent across conditions, it is unlikely that the observed treatment effects were the result of differences in these additional treatment contacts alone. Furthermore, although 39% of participants were self-referred and may have been particularly motivated to engage in an internet-delivered intervention, most participants were clinician-referred and many of the self-referred patients had previous or ongoing contact with CAMHS, suggesting that the sample is clinically representative. Moreover, the lack of data on interrater reliability of the clinician-administered assessments across clinicians and time is an important limitation and precludes determination of the quality of the clinician-rated outcomes (including measures of NSSI and global functioning), thereby threatening the validity of the findings. Nonetheless, replication of findings across self-reported and clinician-assessed NSSI frequency suggests that findings pertaining to the primary outcome of NSSI were not driven solely by rater differences.Likewise, the predominantly female sample and focus on adolescents with NSSID limit the generalizability of our findings. Future studies should examine the efficacy of this treatment among self-injuring adolescents without NSSID and with greater gender diversity. Future studies of IERITA should also include longer follow-up periods of at least 1 year. Moreover, at some weeks, the proportion of missing self-reported weekly data was moderate and the wide variety of observed missing data patterns precluded formal sensitivity analysis (treating data as not missing at random). However, intermittent missing observations are common in clinical trials employing weekly measures, and it is often reasonable to assume that these data points are randomly missing.