This study demonstrates the expected efficacy of a CBT program for individual treatment of OCD. Compared with the waitlist period, treatment saw significant reductions in OCD severity, anxiety and depression levels, and obsessional beliefs. These improvements occurred using a manualised treatment approach administered by trainee therapists under supervision. Completion, recovery and relapse rates compared well with previous research (McKay et al., 2015; Öst et al., 2015). Treatment completion without medication change or drop-out was associated only with lower rates of Major Depressive Disorder. Of particular note, mean YBOCS scores at pre-treatment were greater than 23, while end-treatment YBOCS were below 11. Both scores were similar to those from the most comparable published study using CBT and the self-report YBOCS (Whittal, Thordarson, & McLean, 2005). The recovery rate of 56% for treatment completers, as defined by clinically reliable change (Jacobson & Truax, 1991), is similar to that reported in previous research (50–60% recovery; Fisher & Wells, 2005). Despite this and the degree of symptom reduction, there was still a large proportion of participants who did not respond satisfactorily. After accounting for non-completers and relapsers, the findings highlight the need to search for additional intervention strategies that may enhance treatment. It is essential that we understand what factors determine who is not able to utilise current treatments in a way that impacts on dropout, clinically reliable symptom reduction, and relapse.

Consistent with expectations, findings indicated that higher initial OCD symptom severity was associated with poorer treatment outcome. Using different approaches, both Keeley et al. (2008) and Knopp et al. (2013) reported in their systematic reviews that symptom severity was a predictor of treatment response. For instance, Keeley et al. (2008) identified several studies reporting that greater initial OCD symptom severity was associated with poorer treatment outcomes (e.g. Mataix-Cols, Marks, Greist, Kobak, & Baer, 2002). In contrast, Olatunji et al. (2013) conducted a meta-analysis of CBT and found no relationship between outcome and initial OCD severity. Much of the variation in the literature may be accounted for by the specific type of CBT utilised. Our treatment protocol was based on a combination of ERP and CT, while previous studies have been based on CT (Steketee et al., 2011) or ERP (Steketee & Shapiro, 1995) alone. Furthermore, most previous literature has examined predictors of the extent of change in OCD symptoms rather than clinically significant change or recovery. We found that only pre-treatment OCD severity, was a significant predictor of recovery status. Consistent with our findings, Kempe et al. (2007) used logistic regression models to examine remission as defined by a YBOCS score lower than thirteen combined with a reduction of seven points compared to baseline. They also found that higher pre-treatment OCD severity was associated with poorer likely outcome. This study also used a 16-week treatment period, although their sample included a combination of cohorts undertaking CT, ERP or the combination of these with fluvoxamine. Future research needs to examine the importance of initial OCD severity in both symptom amelioration and recover, but also needs to consider how differing treatment protocols impact on findings.

That treatment completion was associated with incidence of co-morbid major depression is consistent with previous research (Thiel et al., 2014). While major depression was associated with drop-out or medication change, an interesting finding from our research was that this occurred independent of initial level of depressive symptom severity and that neither initial depression or anxiety levels, nor medication status predicted outcome. Perhaps a diagnosis of a MDD is more indicative for recurring or chronic high levels of depressive symptoms as distinct from temporally high levels of self-reported depressive symptoms, and therefore more likely to cause persistent interference in treatment engagement. In general, depression may impact on treatment success through its influence on motivation, behavioural activation and their effects on discouraging ERP. A study by Zitterl et al. (2000) found that as OCD symptoms decreased during CBT intervention, depression levels improved, too, and suggested that comorbid depression is not indicative of treatment prognosis in OCD. Consistent with Abramowitz (2004), our treatment protocol included an initial focus on behavioural activation, activity management and CT for mood problems which may account for our findings.

Given that recent research has highlighted the association between symptomatic amelioration and the adoption of more adaptive beliefs, we were particularly interested in examining cognitive predictors of treatment outcome. We found that conviction in all OCD-related cognitions decreased with treatment and that those changes were maintained at follow-up. While initial OCD-related beliefs did not predict recovery status, we found that changes in all OCD-related cognitions correlated significantly with changes in OCD severity. Of particular note, initial levels of perfectionism and intolerance of uncertainty, as well as changes in this cognitive style, were unique predictors of outcome.

Perfectionism can be conceptualised as involving attempts to minimise mistakes to dispel feelings of uncertainty provoked by one's intrusive thoughts (Obsessive Compulsive Cognitions Working Group, 2005). Perfectionism relating to doubts about one's actions has been found to correlate highly with OCD severity, and recent research has supported the role of perfectionism in impeding response to CBT especially with respect to post-treatment levels of compulsive symptoms (Wilhelm et al., 2015). Such findings are in line with Frost and DiBartolo's (2002) hypothesis that elevated perfectionism and personal rigidity may affect treatment response by interfering with a patient's ability to endure exposure, and therefore to examine the evidence regarding beliefs about intrusive thoughts. An intolerance for uncertainty or “pathological doubt” (Tolin, Abramowitz, Brigidi, & Foa, 2003) may be of importance not only as related to exaggerated beliefs about the probability and cost of unwanted outcomes, but also to heightened feelings of distress when faced with multiple possibilities. In treatment, a de-catastrophising of uncertainty (Tolin et al., 2003) is required which forces a weakening of the association between uncertainty and high levels of anxiety.

Future developments of treatment manuals may need to incorporate a stronger focus on changing perfectionistic beliefs in order to enhance treatment outcomes, possibly early in treatment. Wilhelm et al. (2015) found that changes in perfectionism and intolerance of uncertainty beliefs preceded behavioural symptom reduction for OCD patients and mediated successful treatment response. Furthermore, Manos et al. (2010) reported that change in perfectionism and uncertainty from pre- to post-treatment was a unique predictor for global change in OCD severity. Egan, Wade, and Shafran (2011) proposed perfectionism as a “transdiagnostic process” involved in numerous psychological disorders such as anxiety disorders, depression and eating disorders. Their model describes clinical perfectionism as a vicious cycle stemming from performance related behaviour, (e.g., constant performance checking), and counter-productive behaviours (e.g., avoidance, procrastination). Based on the model of clinical perfectionism, a CBT approach towards treating perfectionism has been developed (Egan, Wade, Shafran, & Antony, 2014). However, ongoing research is also required to further delineate which specific aspects of perfectionism are associated with poorer recovery in order to develop improved treatments. Furthermore, additional theoretical models have been proposed outlining the nature of perfectionism in OCD.

Previous theoretical discourse has identified perfectionism as a defensive strategy for protecting positive internal representations of the self (Guidano & Liotti, 1983). According to this theory, individuals with OCD have an ambivalent sense of self-worth based on early developmental influences and resulting insecure attachments. Hence, they are more likely to notice and become preoccupied with ego-dystonic intrusive experiences which conflict with their implicit sense of moral self. Self-ambivalence has been found to be positively associated with OCD severity and OCD-relevant beliefs such as perfectionism, with some evidence emerging of its relevance to treatment outcomes (Bhar & Kyrios, 2007; Bhar, Kyrios, & Hordern, in press). Bhar et al. (in press) reported that, although not directly addressed in treatment, self-ambivalence was found to predict symptom reduction. It remains to be seen whether a focus on self and morality-related aspect of OCD in treatment effects levels of perfectionism and, hence, improves outcomes. Nonetheless, a range of interventions focusing on the self have recently emerged that may usefully be adapted for OCD. For instance, narrative approaches have been used in the treatment of other anxiety disorders (Gonçalves & Stiles, 2011), while self construals are targeted either implicitly or explicitly in emerging theoretical perspectives and interventions; e.g., dialogical self (Hermans & Gieser, 2012), mindfulness (Segal, Williams, & Teasdale, 2012), Acceptance and Commitment Therapy (Hayes, Strosahl, & Wilson, 2011).

The relapse rate in the current study was too low to allow any reliable statistical analysis of the differences amongst groups. OCD is characterized as a chronic disorder that is prone to relapse particularly in times of high stress. Although the relapse rate of evidence-based psychological treatments for OCD is relatively low generally (e.g. McKay et al., 2015), it is still of importance to determine whether the addition of cognitive techniques might reduce relapse even further. For instance, as yet unpublished data (Bhar, 2004; Kyrios, Hordern & Bhar, 2001) found that resolution of self-ambivalence during treatment was associated with lower relapse in compulsions. Future studies with larger sample sizes might be better able to identify cognitive and self-related factors associated with relapse in order to indicate possibilities for additional intervention strategies.

There is an ongoing need to identify those at risk for poorer outcomes following treatment for OCD in order to develop more effective treatments. The present study identified symptomatic, and cognitive factors that were associated with recovery status as defined by end-treatment severity and clinically reliable change. On the basis of our findings, it would seem prudent for treatments to focus on such factors so as to maximize outcomes. However, we need to be cognisant of the likelihood that specific findings may reflect the nature of the treatments that we utilise and the nature of the cohorts that we treat in our clinics, although they may also point to other factors requiring targeting. At present the treatment outcome prediction literature is littered with inconsistencies, inclusive of how outcome is defined, specific variables used and identified as predictors of outcome, and the precise treatment protocols used. Future research will need to account for such issues before we are able to use the literature in order to base clinical decisions about the type of treatment recommended for individuals presenting with specific characteristics.