Ultimately this is an empirical question. After considering that we can look at the possible advantages in a theoretical sense.
Right now there are a handful of studies that have looked directly and they tend to be medium to small. Only a few are published, and one of these barely mentions outcome because it was a piece on process of change. So we have a long way to go before this question will be answered empirically.
Here are the studies done so far:
Rob Zettle, who trained with Beck, did two very small randomized trials on ACT versus CT for depression – one using individual ACT and CT and the other using ACT and CT group therapy. A larger multi-site randomized trial is underway right now. In his two studies (see the ACT Handout) he found Cohen’s d’s at post between ACT and CT of 1.23 (individually delivered) and .53 (group) and at follow-up of .92 and .75. The N was very small though. The ACT group was only an N of 6 in the individual study and about 10 or so in the group study.
The 4 other studies are brand new and are not published yet. Ann Branstetter did a randomized trial with end stage cancer distress. Ann was trained in traditional CBT and she applied CBT procedures she thought would help (such as cognitive restructuring). There was not follow up because the patients were in end stage cancer but at week 12 ACT had a Cohen’s d of .9 compared to traditional CBT on distress over dying. You can email her for details – she is at Southwest Missouri State University.
Jennifer Block’s dissertation at Albany (she was just hired as a faculty member at LaSalle) compared ACT and CBGT in social phobia and found a Cohen’s d of .45 at post in favor of ACT compared to traditional CBT on the behavioral measure (standing up and speaking).
Carmen Luciano’s team at the University of Almeria just did a smoking trial comparing ACT and a CBT package used by a Spanish cancer society and found a Cohen’s d of .42 at a one year follow up on smoking cessation.
Raimo Lappalainen and his group at the University of Tampere has data in an effectiveness trial comparing ACT and traditional CBT (using CBT methods linked to functional analysis, such as skills training, or exposure) in a training clinic. Beginning student therapists were randomly assigned one ACT and one traditional CBT client (N = 14 each condition). Problems ranged across the usual outpatient spectrum but they were mostly anxiety and depression. On the SCL 90 the post Cohen’s d between ACT and CBT was .62. At follow up the effect was larger. Here is the reference: Lappalainen, R., Lehtonen, T., Skarp, E., Taubert, E., Ojanen, M., & Hayes, S. C. (2007). The impact of CBT and ACT models using psychology trainee therapists: A preliminary controlled effectiveness trial. Behavior Modification, 31, 488-511. By thw ay at the process level there was greater acceptance for ACT patients; great self-confidence for CBT patients. Both correlated with outcomes, but when partial correlations are calculated, only acceptance still relates to outcome. The effect was accidentally not included in the publication but at follow up ACT was now significantly better than CBT in self-confidence.
Evan Foreman and James Herbert reported similar data from their clinic at Drexel University: Forman, E. M., Herbert, J. D., Moitra, E., Yeomans, P. D. & Geller, P. A. (2007). A randomized controlled effectiveness trial of Acceptance and Commitment Therapy and Cognitive Therapy for anxiety and depression. Behavior Modification, 31(6), 772-799. In this study 101 heterogeneous outpatients reporting moderate to severe levels of anxiety or depression were randomly assigned either to traditional CT or to ACT. 23 junior therapists were used. Participants receiving CT and ACT evidenced large and equivalent improvements in depression, anxiety, functioning difficulties, quality of life, life satisfaction and clinician-rated functioning. “Observing” and “describing” one’s experiences mediated outcomes for those in the CT group relative to those in the ACT group, whereas “experiential avoidance,” “acting with awareness” and “acceptance” mediated outcomes for those in the ACT group.
It is also known that ACT methods can empower behavioral methods (which are also part of the ACT model by the way ... so this finding is in essences a confirmation of the model itself). For example, consider this study: Levitt, J. T., Brown, T. A., Orsillo, S. M., & Barlow, D. H. (2004). The effects of acceptance versus suppression of emotion on subjective and psychophysiological response to carbon dioxide challenge in patients with panic disorder. Behavior Therapy, 35, 747-766. In it acceptance methods (drawn directly from the ACT book) did a better job than control strategies in promoting successful exposure to CO2 gas in panic disordered patients.
A similar finding was reported in:
Campbell-Sills, L., Barlow, D. H., Brown, T. A., & Hofmann, S. G. (2006). Effects of suppression and acceptance on emotional responses of individuals with anxiety and mood disorders. Behaviour Research and Therapy, 44, 1251-1263. As with the study above, brief acceptance methods led to lower heart rate during exposure to an aversive film and less negative affect during the post-film recovery period that did control strategies in individuals with anxiety and mood disorders.
So far it looks as though there might be a small advantage for ACT over traditional CBT methods in outcomes; there is a different set of change processes involved, and ACT methods may empower traditional behavioral methods.
Theoretically, the strengths of the ACT model as compared to CBT are these.
1. The model is easily scalable and broadly applicable. If you look at the whole outcome literature done so far (RCTs, controlled time series designs, and case studies) the problems targeted form a pretty broad list: PTSD, panic, depression, racist prejudice, burnout, epilepsy, smoking, OCD, pain, psychosis, cancer, diabetes, multiple sclerosis, sports psychology, attitudes against pharmacotherapy, skin picking, learning new procedures at work, heroin abuse, worksite stress, work innovation, marijuana abuse, and several others.
2. The putative processes of change are well specified with at least marginally adequate measures available in most areas. These change processes are a small set and they do not wildly vary from disorder to disorder.
3. The mediational analyses seem to be working. There are by our count already 16 successful formal mediational analyses published, or completed and coming. So far the data are very supportive. The processes successfully examined so far include acceptance, defusion, values, committed action, and psychological flexibility so most of the key ACT have some data in mediational trials.
4. Specific components seem to be working when inductively tested. There are at least 18 such studies. In every case ACT methods are impactful and work in a way that is theoretically coherent. These include all 6 points of the hexagon model.
5. The basic theory is intricately linked with the technology and itself seems to be working. For example, we are approaching 10 RFT studies linked to the three senses of self in ACT; RFT work on values is coming; and so on.
For those who believe only in RCTs of manuals, much of this answer will be dismissed. But the history of science shows that you cannot create a progressive science using only outcome studies. I (SCH) explained why in The Scientist-Practitioner (Hayes, Barlow, & Nelson-Gray, 1999). In a nutshell, though, it is this: without good theory, the technological development problem is based on common sense categories and it becomes empirically and practically overwhelming.
This should not be heard as “ACT adherents say RCTs are not important.” ACT folks have published nearly 30 RCTs of ACT methods. But they are not enough! Development in the areas of philosophy of science, basic principles, applied theory, specification of processes of change and effectiveness are just as important (and in the long run more important) than efficacy tests of technology.
The scientific game the ACT / RFT / Contextual psychology group is playing is this: to try to create a truly progressive science of psychology that can address the human condition in a more adequate way. Sure that is bold, but why not have bold goals? Is the ACT group willing to stand or fall on RCTs as a measure of success? Ultimately yes. But we want and demand another, even more difficult criteria: seeing a more truly useful psychology emerge as a result. That means concepts, theories, components, basic principles, effectiveness, training, dissemination and so on.
We think it is only fair to insist that ACT be measured against its own very difficult criteria when considering the progress of this effort. For example, examining ACT without examining RFT is like examining a cancer drug without looking at physiology.
Like the hare and the tortoise, ACT is following the slow and steady path. We think traditional CBT hopped ahead into a lay theory of cognition -- which produced quick progress but long term problems. We'd rather take the slow, one step at a time approach of contextual behavioral science. Which one will go farthest? Let's see. Let's be patient and see.
If there is an advantage of the ACT wing of CBT as compared to traditional CBT, this is where you are most likely to see it.