Cooper, M. (2010). Essential Research Findings in Counselling and psychotherapy.London: SAGE

It is primarily believed within cognitive-behavioural psychotherapy (CBT) that the psychological approach has a importance for the outcome of therapy.

Empirically supported treatments (ESTs); therapeutic practice that have been shown to be effective for a certain group of clients, through clinical intervention studies, where it has been shown to have a better effect than no treatment or as good as another validated treatment method.

CBT is the approach that have the best effect for most disorders. However there is some issues concerning the fact that many clients does not live up to the demands for a diagnose or the great comorbidity of diagnoses. In addition to this, results from these studies is not very generalisable, as the majority of clients does not live up to the inclusions criteria as well as most participants are white or European. CBT is easier to test than other approaches and therefore studies of many different approaches are still missing. The shortage of evidence is not the same as counter-evidence.

Researcher allegiance effect; the tendency for a researcher to find what supports their own attitudes, expectations and preferences. A solution to this could be double-blinded studies.

Dodo bird finding: that the therapy approaches’ effect does not variate very much from each other, only about 0.2, which is a small effect size and can be caused by errors like researcher allegiance effect.

Bona fide therapy: a therapeutic practice offered in good faith, like a practice where the therapist is trained and committed to an approach with healthy, responsible psychological principles.

Non-specific or common factors: aspects of therapy that are common for most therapeutic approaches, like the therapeutic relation.

Specific model factors: well defined actions that the therapist performs that is associated with a specific therapeutic approach.

Contra arguments to the dodo bird verdict: different clients get different outcomes of the different psychological approaches. Different approaches helps differently on different disorders or diagnoses. Many meta-studies shows that CBT has a greater effect, also even if the effect size is only 0.2 different from the other approaches. There is a shortage of evidence to show that some approaches are better than others. Researcher allegiance effect can not compensate the results of meta-studies that favourites CBT. That some therapy approaches gets more financial support and are scientific investigated more is because there is something to them.

Both common and specific factors brings something to therapy. Lambert did find that 85 % of therapy outcome is caused by common factors where specific factors only cause 15 % of the effect.

Patient uniformity myth: that all clients has a need for the same things.

Aptitude-treatment interaction (ATIs): investigate which treatment have the best effect for patients with specific traits.