Cognitive Therapy v Exposure in OCD PTSD and PD
This meta-analysis provided no evidence of a statistically significant difference in efficacy between exposure and cognitive therapy for the clinically relevant outcome measures across RCTs studying OCD, PTSD, and panic disorder with or without agoraphobia.
This does not mean that cognitive changes do not mediate the treatment response as it is possible that cognitions could change and mediate treatment through means other than cognitive therapy. Cognition changes in the trials of pharmacotherapy have indeed been demonstrated [42
]. Behavioural work could also result in cognitive changes even in the absence of direct cognitive therapy [43
]. There is also growing evidence of the role cognitive mediation might play in achieving clinical improvement during exposure therapy [44
Equally, it is possible that exposure plays an important role in some cognitive interventions, behavioural experiments in particular.
In addition, it is possible that the different components of CBT examined in this study may work on different systems, such that producing change in one system (for example, the behavioural system) will produce changes in other systems (such as the cognitive system) [41
]. If this was the case then it is not surprising that component analysis studies show similar outcomes for exposure and cognitive therapy in many conditions.
Cognitive Therapy v Exposure in Social Phobia
CT was found to be superior to E in both short term and long-term outcomes in Social Phobia (effect size differences from 0.28 to 1.01). A re-evaluation of the data using a random effects analysis did not change the overall conclusion. This differential efficacy has not been shown previously and is potentially of significant clinical importance. The apparent superiority of CT versus E in social phobia needs to be accepted cautiously. First, the studies included in this meta-analysis were conducted by two research groups that may be especially proficient in the use of cognitive therapy. Second, E condition in two of the three studies was individual, whereas it may be more effective in group setting. Having said this, E condition in all three studies demonstrated significant effect size (0.56- 1.46) and in one study was based on a manual developed by the investigators and tested in previous studies [38
It may be that the nature of social phobia makes cognitive interventions especially important in this condition. The effect of CT may be mediated by an early change in estimated social cost [38
] partly explaining the long-term CT superiority over E. In addition, there are studies demonstrating that behavioural experiments may be more effective in anxiety reduction than exposure alone [46
] particularly when an external focus of attention is used for confronting social anxiety-provoking situations. Exposure in social phobia may be of limited value without some skills-based behavioural response. It is also possible that the duration of exposure in social phobic situations is not sufficient for it to be effective as many social encounters have brief duration. Cognitive therapy draws on a range of techniques to achieve therapeutic change, some of which have already been demonstrated to be superior to exposure alone. For instance, the impact of video feedback, imagery work and the negative consequences of self-directed attention have all been demonstrated experimentally [47
]. In summary, CT appears to be more effective than exposure alone in social phobia; however more studies from a range of research groups are needed to confirm this finding.
Is there a need to challenge thoughts in CBT?
Since there is no evidence of differential efficacy of CT and E for some conditions, is it therefore necessary to employ cognitive interventions in the treatment of anxiety disorders? The arguments in favour of this proposition could be summarised in this way. 1. There is some evidence that cognitive interventions and behavioural interventions have similar effect sizes for certain conditions [10
] or there is even a superiority of modified behavioural interventions compared with purely cognitive interventions [49
]. 2. The rapid response argument [50
] centres on the idea that many patients show an improvement early in the course of CBT [51
] making the effect of cognitive interventions an unlikely mediator of this change (on the assumptions that cognitive interventions require several weeks to be implemented fully) 3. The mediation argument proposes that there is no compelling evidence demonstrating that cognitive change is the underlying mechanism of improvement in CBT. 4. The cost-effectiveness argument where behavioural interventions are seen as cheaper to teach and to implement.
This meta-analysis contributed to the discussion on the first of these points. It would appear that even within the field of anxiety disorders there is no categorical evidence of equivalence between cognitive and behavioural interventions and it may be that cognitive and behavioural interventions may be more suitable for certain conditions. Having said this there was no evidence of a difference in effect size between CT and E in three out of four anxiety conditions.
The rapid response argument would appear to be the weakest of the four. There is plenty of evidence documenting cognitive changes early in the cognitive treatment [33
]. In addition, there is more and more evidence of cognitive change not being specific to cognitive therapy [42
The mediation argument is the most complex one as the criteria for mediation differs depending on the study design [53
]. For RCTs the test of mediation is proposed to include these variables: (1) the proposed mediator correlates with treatment assignment; (2) the mediator has either a main or interactive effect on outcome; and (3) changes in the mediator variable precede changes in the dependent variable. Very few studies address all of these criteria. In addition the issue is confounded by the rapid response phenomenon. The literature on cognitive change as a mediator of improvement is growing, although it remains somewhat inconsistent [38
]. Future studies are likely to clarify the mechanisms of change in CBT further.
The cost-effectiveness argument is the least well studied. There is some evidence of a greater cost of teaching a range of cognitive skills as opposed to exposure alone. The cost of implementation of exposure versus cognitive therapy is also poorly studied but is likely to be lower. It is worth mentioning that all but one of the studies included in this meta-analysis allocated equal time to both CT and E treatment. The studies of relative cost-effectiveness of E versus CT are timely.
The results of a meta-analysis depend firstly on the results of the individual studies included. Therefore, their limitations should be mentioned here first. The studies with very high risk of bias (e.g. with very high drop-out rates) were excluded from the review. Although only RCTs were included, some would appear to have had 'weaker' designs than the strongest ones that exist. This was done to enhance external validity. In half of the studies it was uncertain whether or not outcome assessment was adequately blinded. Similarly, concealment of allocation was often uncertain. In addition no standardised quality assessment tools were used to assess the quality of the studies included. One significant limitation of most studies included is the lack of an explicitly designated a-priori primary outcome measure. None-the-less the outcome measures included in the meta-analysis were either designated as primary or have been well validated in other studies.
Although great care was taken to include pure cognitive therapy versus pure exposure approach to treatment it is possible that a certain amount of E and CT were used across the comparison studies. In addition the effect of adding CT to E (or E to CR) was not studied in this meta-analysis. Based on that, a logical and useful next step in this field of research would be to examine the additive value of E and CT across different conditions.
Only the principal clinical efficacy outcomes were examined in this meta-analysis. On one hand this allowed for a comprehensive and straightforward comparison of two commonly used techniques. On the other hand, it may be that comparing the outcomes other than clinical efficacy (for example depressive symptomatology, drop out rates or quality of life measures) could have contributed to a different interpretation of the results.
The potential impact of researcher allegiance has been much debated in psychotherapy research [56
]. Although it was not the focus of this review, it should be mentioned here as a potential limitation. It is plausible to assume that most studies in this review were carried out by researchers who have positive allegiances to either cognitive or behavioural interventions. However, the high consistency of the efficacy identified in this review makes bias from researcher allegiance unlikely.
Finally, the small number of studies with small sample size deserves mentioning as a limitation coupled with selected demographic characteristics of the subjects (primarily Caucasian adults) and the treatments delivered mainly by highly trained therapists in the centres of excellence. These factors reduce the generalisability of the findings of this meta-analysis and limit the potential for sensitivity analyses on possible confounding variables or predictor variables.
Implications for Practice
The findings of this review have several implications for practice. First, they underline the value of CBT as an effective treatment in mental health care. Second, the findings imply that there is no evidence of statistically significant difference in E versus CT across several but not all conditions. It has to be noted, however, that the extent of individual benefit from E versus CT might vary from patient to patient. Some may respond better to one of the two interventions and some might do better with a combination.
The lack of difference of efficacy between E and CT in OCD, PTSD and PD is important for clinical reasons. The British NICE guidelines state that ERP must be offered as part of CBT for OCD. The guideline development group conducted several comparisons, however only one study was used to compare the efficacy of CT v ERP [57
]. This study showed no significant difference in the initial analysis of the efficacy of CT v ERP (these findings were used for the present study); however after adjustment for medication use a marginally significant result was reported in favour of ERP (p = 0.049). Further studies are required to inform the NICE recommended interventions for OCD
The NICE guidelines for PTSD recommend the use of trauma-focused CBT or EMDR as a first line psychological treatment. Equal efficacy of CT versus E reported in this meta-analysis is in line with this recommendation.
The NICE guidelines on the management of Panic Disorder also recommend CBT as the first line psychological treatment with no specific recommendation of exposure or cognitive therapy as an important ingredient. The comparisons between cognitive and behavioural interventions used to inform the guideline development was based on two studies [30
] one of which was excluded from this meta-analysis due to the main outcome measure not being reported [58
At present there are no NICE guidelines on the management of social phobia. Clinicians might like to note the relative superior efficacy of cognitive therapy over exposure found in this meta-analysis.
A further implication for practice, the lack of evidence for a difference of efficacy between E and CT in PD, OCD and PTSD raises the question of differential indication for behavioural versus cognitive treatment. If E v. CT is not the main determinant of the effect of CBT, then what other criteria might be more fruitful in determining who should receive a particular CBT intervention? Psychotherapy researchers have argued that factors such as the match between therapist and client and the client's motivation for a specific type of therapy should be recognised more [59
]. The use of such "soft" indications can often be more fruitful than an uncritical 'prescription' based on the availability or the services and the therapists' allegiance. For policy makers it will be important to take into account the findings of this review to consider the relative need of training in E v. CT.
There are no good studies documenting the economic implications of teaching and supervising CT v. E and it may be important to undertake such studies especially bearing in mind the recent government initiatives promoting wider use of CBT in the UK and elsewhere.