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Is there an excess of significant findings in published studies of psychotherapy for depression?

Flint J, Cuijpers P, Horder J, Koole SL, Munafò MR - Psychol Med (2014)

Bottom Line: The average statistical power to detect the effect size indicated by the meta-analysis was 49%.Similar results were obtained when these analyses were restricted to studies including a cognitive behavioural therapy (CBT) arm.The small average size of individual psychotherapy studies is only sufficient to detect large effects.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Trust Centre for Human Genetics,University of Oxford,UK.

ABSTRACT

Background: Many studies have examined the efficacy of psychotherapy for major depressive disorder (MDD) but publication bias against results may exist in this literature. However, to date, the presence of an excess of significant findings in this literature has not been explicitly tested.

Method: We used a database of 1344 articles on the psychological treatment of depression, identified through systematic search in PubMed, PsycINFO, EMBASE and the Cochrane database of randomized trials. From these we identified 149 studies eligible for inclusion that provided 212 comparisons. We tested for an excess of significant findings using the method developed by Ioannidis and Trikalinos (2007), and compared the distribution of p values in this literature with the distribution in the antidepressant literature, where publication bias is known to be operating.

Results: The average statistical power to detect the effect size indicated by the meta-analysis was 49%. A total of 123 comparisons (58%) reported a statistically significant difference between treatment and control groups, but on the basis of the average power observed, we would only have expected 104 (i.e. 49%) to do so. There was therefore evidence of an excess of significance in this literature (p = 0.010). Similar results were obtained when these analyses were restricted to studies including a cognitive behavioural therapy (CBT) arm. Finally, the distribution of p values for psychotherapy studies resembled that for published antidepressant studies, where publication bias against results has already been established.

Conclusions: The small average size of individual psychotherapy studies is only sufficient to detect large effects. Our results indicate an excess of significant findings relative to what would be expected, given the average statistical power of studies of psychotherapy for major depression.

No MeSH data available.


Related in: MedlinePlus

Flowchart of inclusion of studies.
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fig01: Flowchart of inclusion of studies.

Mentions: We used a database of 1344 articles on the psychological treatment of depression that has been described in detail elsewhere (Cuijpers et al.2008b, 2011), and that has been used in a series of earlier published meta-analyses (www.evidencebasedpsychotherapies.org). This database is continuously updated through comprehensive literature searches (currently from 1966 to January 2012). We examined 13 407 abstracts identified from PubMed (3320 abstracts), PsycINFO (2710), EMBASE (4389) and the Cochrane Central Register of Controlled Trials (2988). These abstracts were identified by combining terms indicative of psychological treatment and depression (both MeSH terms and text words). We also searched the primary studies from 42 meta-analyses of psychological treatment for depression to ensure that no published studies were missed. From the 13 407 abstracts, we identified 9860 unique abstracts after the removal of duplicates. Of these, 8516 were excluded based on the title and abstract, so that 1344 full-text articles were retrieved for possible inclusion in the database. Of these, 1164 articles were excluded (Fig. 1), resulting in the inclusion of 180 articles in the database.Fig. 1.


Is there an excess of significant findings in published studies of psychotherapy for depression?

Flint J, Cuijpers P, Horder J, Koole SL, Munafò MR - Psychol Med (2014)

Flowchart of inclusion of studies.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4301215&req=5

fig01: Flowchart of inclusion of studies.
Mentions: We used a database of 1344 articles on the psychological treatment of depression that has been described in detail elsewhere (Cuijpers et al.2008b, 2011), and that has been used in a series of earlier published meta-analyses (www.evidencebasedpsychotherapies.org). This database is continuously updated through comprehensive literature searches (currently from 1966 to January 2012). We examined 13 407 abstracts identified from PubMed (3320 abstracts), PsycINFO (2710), EMBASE (4389) and the Cochrane Central Register of Controlled Trials (2988). These abstracts were identified by combining terms indicative of psychological treatment and depression (both MeSH terms and text words). We also searched the primary studies from 42 meta-analyses of psychological treatment for depression to ensure that no published studies were missed. From the 13 407 abstracts, we identified 9860 unique abstracts after the removal of duplicates. Of these, 8516 were excluded based on the title and abstract, so that 1344 full-text articles were retrieved for possible inclusion in the database. Of these, 1164 articles were excluded (Fig. 1), resulting in the inclusion of 180 articles in the database.Fig. 1.

Bottom Line: The average statistical power to detect the effect size indicated by the meta-analysis was 49%.Similar results were obtained when these analyses were restricted to studies including a cognitive behavioural therapy (CBT) arm.The small average size of individual psychotherapy studies is only sufficient to detect large effects.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Trust Centre for Human Genetics,University of Oxford,UK.

ABSTRACT

Background: Many studies have examined the efficacy of psychotherapy for major depressive disorder (MDD) but publication bias against results may exist in this literature. However, to date, the presence of an excess of significant findings in this literature has not been explicitly tested.

Method: We used a database of 1344 articles on the psychological treatment of depression, identified through systematic search in PubMed, PsycINFO, EMBASE and the Cochrane database of randomized trials. From these we identified 149 studies eligible for inclusion that provided 212 comparisons. We tested for an excess of significant findings using the method developed by Ioannidis and Trikalinos (2007), and compared the distribution of p values in this literature with the distribution in the antidepressant literature, where publication bias is known to be operating.

Results: The average statistical power to detect the effect size indicated by the meta-analysis was 49%. A total of 123 comparisons (58%) reported a statistically significant difference between treatment and control groups, but on the basis of the average power observed, we would only have expected 104 (i.e. 49%) to do so. There was therefore evidence of an excess of significance in this literature (p = 0.010). Similar results were obtained when these analyses were restricted to studies including a cognitive behavioural therapy (CBT) arm. Finally, the distribution of p values for psychotherapy studies resembled that for published antidepressant studies, where publication bias against results has already been established.

Conclusions: The small average size of individual psychotherapy studies is only sufficient to detect large effects. Our results indicate an excess of significant findings relative to what would be expected, given the average statistical power of studies of psychotherapy for major depression.

No MeSH data available.


Related in: MedlinePlus