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Wednesday, 3 July 2013


Clinical Psychology and Psychotherapy

Clin. Psychol. Psychother. 16, 510–522 (2009)

Published online 2 September 2009 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/cpp.648

The Dodo Bird Verdict—Controversial,

Inevitable and Important: A Commentary on 30

Years of Meta-Analyses

Rick Budd1 and Ian Hughes2*
1 Ludlow Street Healthcare, Llanbedr Court, Newport, Wales, UK
2 Psychology Department, Cardiff and Vale NHS Trust, Cardiff, Wales, UK

 The Dodo Bird Verdict—Controversial, Inevitable and Important: A Commentary on 30 Years of Meta-Analyses

Rick Budd1 and Ian Hughes2*

1 Ludlow Street Healthcare, Llanbedr Court, Newport, Wales, UK

2 Psychology Department, Cardiff and Vale NHS Trust, Cardiff, Wales, UK

In this article, the assertion that different psychological therapies are of broadly similar efficacy—often called the ‘Dodo Bird Verdict’—is contrasted with the alternative view that there are specifi c therapies that are more effective than  others for particular diagnoses. We note that, despite thirty years of meta-analytic reviews tending to support

the finding of therapy equivalence, this view is still controversial and has not been accepted by many within the psychological therapy community; we explore this from a theory of science perspective. It is further argued that the equivalence of ostensibly different therapies is an inevitable consequence of the methodology that has dominated

this field of investigation; namely, randomised controlled trials

[RCTs]. The implicit assumptions of RCTs are analysed and it is

argued that what we know about psychological therapy indicates that it is not appropriate to treat ‘type of therapy’ and ‘diagnosis’as if they were independent variables in an experimental design. It is noted that one logical consequence of this is that we would not expect RCTs to be capable of isolating effects that are specific to ‘type of therapy’ and ‘diagnosis’. Rather, RCTs would only be expected to be capable of identifying the non-specific effects of covariates, such as

those of therapist allegiance. It is further suggested that those nonspecific effects that have been identified via meta-analysis are not trivial findings, but rather characterise important features of psychological therapy.



As has been argued above, the failure of RCTs

(and the meta-analyses of RCTs) to partition out

any specifi c effects of psychological therapy to different

types of interventions (even when diagnosis

has been controlled for) is attributable to the fact

that it is exceptionally diffi cult to operationalize

and control this independent variable. That is to

say that despite rigorous attempts at manualization

the evidence suggests that it is not possible to

ensure that different therapies do not share such a

large proportion of active therapeutic ingredients

as to dilute the power of RCTs to isolate treatmentspecifi

c effects. Moreover, and perhaps even more

signifi cantly, it is impossible to ensure that different

interventions do not affect the same psychological

mechanisms of change, thus similarly limiting the

power of RCTs to isolate treatment specifi c effects.

When these limitations are combined with the fact

that diagnoses are overlapping, ‘fuzzy’ concepts,

which do not adequately control for psychological

factors (e.g., sub-clinical personality features, etc.)

that are likely to interact with the type of intervention

in determining its effi cacy, it is not surprising

that the Dodo Bird Verdict has survived for more

than 30 years. In short, its survival rests on the fact

that while RCTs (and the meta-analysis of data

obtained from RCTs) are capable of demonstrating

that psychological therapy as an aggregate is effective,

they are not capable of identifying the specific

elements of therapy that are effective for different


From the research perspective the clarion call

is clear. RCTs do not represent an objective ‘gold

standard’ of research, but rather, are simply one

of many research methodologies, which, like all

methodologies, have their strengths and weaknesses.

When used to test causal relationships

between a dependent variable and a set of independent

variables that can be adequately defi ned

and operationalized, there is no alternative to constructing

an RCT. However, for addressing other

research questions, such as ‘how does psychological

therapy help different people change?’ different

methodologies could be more appropriate (e.g.,

Pachankis & Goldfried, 2007).

Moreover, there is a need to move away from

designing psychological interventions targeted

at an invalid psychiatric nosology, to developing

interventions directed at alleviating distressing

experiences (e.g., low mood, intrusive memories)

or which are directed at changing problematical

behaviours (e.g., avoidance, rumination). These

interventions need to be developed in light of our

understanding of the psychosocial processes that

maintain them. How and when they are used in

therapy needs to be informed by a full understanding

of the individual therapy process.

To illustrate our favoured approach, let us consider

‘depression’. Typically, within the present,

diagnostically driven approach, patients diagnosed

as having ‘depression’ are offered a package—

often of around 20 sessions—of CBT treatment,

which comprises a number of almost invariant elements

(e.g., activity scheduling, thought diaries,

thought challenging). We consider that such an

approach ignores the variability and complexity

of the symptoms of people diagnosed as having

‘depression’, and that it also ignores the psychosocial

factors maintaining the symptoms (e.g.,

family relationships, employment problems, thebroader environmental context); and, that it also

ignores the therapeutic relationship. Low mood,

for instance, is a very common feature of ‘depression’.

In order to ameliorate it, we would advocate

a detailed analysis of its maintaining factors on

an individual basis, and then the application of

an appropriate technique (e.g., increasing activity

levels or resolving relationship confl icts or exploring

the validity of negative automatic thoughts).

But, importantly, this needs to be done within

the context of the therapeutic process, that is to

say, at an appropriate time, and in a way that is

most likely to promote change within the client.

(A similar general approach is much more fully

described in the important chapter by Norcross

and Beutler [2008]).

Most importantly we need to reject the medical

model, cease to view therapy as being like a drug

that is given to clients and, instead, view it for what

it is, a social infl uence process that occurs (most

typically) between two people.

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