The dodo bird might be extinct in the real world but in the world of
psychotherapy research it refuses to die. However, a group of German
researchers recently put forward an article were they had randomized
patients to either a PDT or CBT condition and measured the relative
proficiency of the two orientations, and they found that their results
delivered a convincing blow to the dodo bird verdict.
The dodo bird verdict is the long held belief by some researchers and
clinicians that all psychological interventions produce the same
outcome. The proponents of this theory often attribute the efficacy of a
therapy to “common factors”, such as the alliance between therapist and
client. This is in opposition to crediting the success of a therapy to
the specific techniques used by the therapist, e.g. exposure or
It’s no secret that the main rivalry has been between cognitive behavior
therapy (CBT) and psychodynamic therapy (PDT) practitioners. However,
one of the issues with testing the dodo bird verdict has been the lack
of quality studies on the efficacy of PDT. More importantly very few
direct comparisons have been made within randomized controlled trails.
Therefore it’s always exciting when a research group puts forward
Watzke et al. (2012) recruited 189 patients and randomized them to
either CBT or PDT, they used a 3:2 ratio because the facilities had less
capacity to give PDT. The study took place in a natural setting at an
inpatient unit in Germany, and because of the naturalistic setting very
broad inclusion criteria were used. The treatments were administered as
brief group therapies, with 3-4 sessions per week and an average
treatment length of 6 weeks. Both treatment groups additionally received
one individual session per week. No treatment manuals were used and the
therapists received no special training for this study.
The primary outcome used in the study was the General Severity Index of
the Symptom Check list-14 (SCL-14). The secondary outcomes was mental
component summary of the SF-8, and the Inventory of Interpersonal
Problems (IIP-C). The outcomes were assed at intake and at 6 month
You can see their results in Figure 1, were I’ve made a plot of the
results, and calculated Cohen’s d with 95 % CIs.
In this direct comparison between CBT and PDT, CBT clearly performed
better, and quite convincingly so. Clearly the dodo bird did not fair
well in this study, but more research like this is needed before the
dodo bird finally can be put to rest. If indeed CBT is more effective
than PDT, then this is incredible valuable research for all the patients
out there. Hopefully we’ll see more randomized controlled trails that
compare two bona fide psychotherapies in the future.
Quality of the evidence
This study is a randomized controlled trail and as such the evidence has
got the potential to be of high quality. Some aspects of the study are a
bit unclear though, for instance the authors never describe how the
allocation sequence was concealed. And I couldn’t see any information on
why they only hade two time points (baseline and 6 months), more time
points would’ve provided more information. Additionally, I think they
should’ve analyzed their data as a multilevel model, especially if they
used many different therapists and different hospital units. Also, they
did not state how many therapists that were used in the study, and
consequently they did not test for any therapist interaction effect.
However, the authors explicitly state that the treatments were not
recorded and hence no assessment of adherence or competence was made.
Though, the “results of a prior study including independent expert
raters (video ratings) describe the main interventions of both
treatments (Watzke et al, 2004, 2008) and suggest that there was
sufficient treatment differentiation between the two treatments in the
unit”. So it’s possible that the outcome is due to the CBT therapists
being more competent, and not due to CBT being more effective as a
specific intervention. However, to me this seems redundant as from my
perspective it’s a sign of competence to choose CBT before PDT. This
statement might seem unnecessary polemic, but CBT is the treatment of
choice for many disorders today with a vast amount of research
supporting its efficacy, so perhaps one must be a bit scientific naïve
to administer PDT for diagnoses were research support is lacking.
The researchers used unequal groups, with a 2:3 ratio (CBT having more
patients). It’s hard to estimate if this had any effect on the outcome,
statistically this might affect the significance test if the assumptions
of homogeneous variance is violated. However, by looking at the standard
deviations reported in the study this doesn’t seem to be a problem.
Moreover, the authors performed analysis to test if any cofounders might
have been unequally distributed between the treatments, and found no
evidence for this. Also, attrition didn’t seem to be a problem, the
authors performed sensitivity analyses and intention-to-treat analyses,
which did not reveal any cause for concern.
I’m not sold on the outcomes they assessed. I’m thinking that they
could’ve used more outcome measures, for instance they could’ve assessed
depression and anxiety separately. However, there’s evidence that the
SCL-scales are quite good at detecting general symptom severity.
Overall, I find the results of this study interesting and I don’t think
any of the study’s shortcomings invalidates its findings. But as always
more studies are needed before any robust conclusion can be made.
B, Rüddel H, Jürgensen R, Koch U, Kriston L, Grothgar B, & Schulz H
(2012). Longer term outcome of cognitive-behavioural and psychodynamic
psychotherapy in routine mental health care: Randomised controlled
trial. Behaviour research and therapy,
50 (9), 580-587 PMID: 22750189