The challenge in meta-analyzing psychological treatments is that there is a lack of what's called "homogeneity" in both treatments and conditions. Treatments could include ones as methodical as cognitive therapy; it could include ones as unstructured as conversations with a counselor; or, it could include in-between treatments, such as classic Freudian psychoanalysis, which involves exploring the meaning behind dreams or negative thoughts.

The consensus in the scientific community is that "cognitive therapy works."

There isn't consensus among ordinary people that "talk therapy works."

Definitions

Google defines psychotherapy as "the treatment of mental disorder by psychological, rather than medical means." But per this Psychology Today article, psychotherapy is referred to as "an umbrella term for any professional who is trained to treat people for their emotional problems." Presumably this could involve medication.

Diagnostic types

This meta-analysis focused on these six diagnostic categories:

• mood disorders
• anxiety
• post-traumatic stress disorder
• eating disorders
• personality disorders
• substance use disorders

Studiable treatment types

Cujipers's meta-analysis (see citation below), looked at 91 studies in the past three decades that randomly assigned patients to two or more treatment options for mild to moderate adult depression. Of the 91, the following treatment options appeared n times, which provides some signal as to what "works."

• Cognitive-behavior therapy (31)
• Nondirective supportive treatment (20)
• Behavioral activation treatment (15)
• Psychodynamic treatment (10)
• Problem-solving therapy (7)
• Interpersonal psychotherapy (6)
• Social skills training (5)

Meta-analyses

From Google

Top results (as of 2 Nov 2018) when you Google "meta-analysis psychotherapy":

• Pim Cuijpers (Dec 2008) Psychotherapy for depression in adults: a meta-analysis of comparative outcome studies [Full Text]

  • It doesn't say whether or not psychotherapy as a whole is effective, but it does say that it's unclear as to which of the tentpole non-drug interventions stands out better than the others.
  • Pim Cuijpers is Head of the Department of Clinical, Neuro and Developmental Psychology at the Vrije Universiteit Amsterdam (€480M endowment per year, one of two large publicly funded universities in Amsterdam)
  • Found 91 studies with psychological therapies randomly assigned to different treatment options, such as CBT or Nondirective Support Therapy.

• Pim Cuijpers (Oct 2014) Psychotherapy for subclinical depression: meta-analysis

  • mild-to-moderate effect size and 39% to 26% reduction in risk of major depressive episode
  • Most treatments were CBT

• Alice X. Huang (Mar 2015) A systematic review and meta-analysis of psychotherapy for late-life depression

  • Patients 55 years or older

• Glen Spielmans (Mar 2011) Moderators in psychotherapy meta-analysis

  • A discussion on how to improve meta-analysis in psychotherapy

Other Meta-analyses:

• Glen Spielmans (Mar 2011) Psychotherapy versus second-generation antidepressants in the treatment of depression: a meta-analysis

  • Says that SGAs are better

• Ken Pope's index of Psychological Interventions

Meta-reviews (review of meta-analyses)

• Georg E. Matt (1997) What meta-analyses have and have not taught us about psychotherapy effects: a review and future directions.
  • Old, but describes problems with incorporating meta-analyses
  • example: There is mounting evidence suggesting that biases associated with individual studies do not cancel each other out when studies are combined meta-analytically

Meta-analyses can disagree

Among interventions for treating trauma in children and adolescents, eye movement desensitization and reprocessing was awarded the top rating (well supported) by the California Evidence-Based Clearinghouse for Child Welfare but the lowest rating (no support) by the Hawaii Blue Menu of Evidence-Based Child and Adolescent Psychosocial Interventions (Hennessy 2013)

Cochrane

Cochrane is the gold standard for meta-analysis, and therefore the closest thing we have to truth in understanding evidence-based outcomes.

Systematic reviews

Sharea Ijaz (May 2018): Are psychological therapies effective in treating depression that did not get better with previous treatment?

Comments and criticisms

Pablo Luis Lopez (Sep 2018): Overcoming the difficulties of meta-analysis in psychotherapy - Lopez reviewed Cochrane's library and noticed that its yearly publication of systematic reviews (SR) and meta-analyses (MA) has slightly declined whereas PubMed's SRs and MAs has gone up significantly. He wasn't exactly making a criticism per se, but rather making a call for consensus for solving heterogeneity issues with psychotherapy studies.

Sharon Green-Hennessy (Jan 2013): Cochrane Systematic Reviews for the Mental Health Field: Is the Gold Standard Tarnished?

Cochrane's future

The Cochrane Collaboration is a consortium of Cochrane centres scattered across different institutions. On 17 Sep 2018, Peter Gøtzsche, the director of Cochrane's Nordic centre was expelled from the Cochrane Collaboration's governing board due to his protestations about Cochrane cozying up to Industry. Four elected members resigned along with Gøtzsche, thus triggering Cochrane's charter rules and leading to the resignation of two appointed members. In other words, Gøtzsche's expulsion led to the board shrinking from thirteen to six members.

Gøtzsche was expelled after posting "A moral governance crisis: the growing lack of democratic collaboration and scientific pluralism in Cochrane" on Cochrane's website. Cochrane has since pulled the letter down.

Conspiracy theory

When you Google "Cochrane review cognitive therapy" (as of 2 Nov 2018), the first result is Cognitive behavioural therapies versus treatment as usual for depression. However, on 22 Oct 2018, the review was updated to say that it had been withdrawn. The apparent reason is they are consolidating and updating their review for cognitive therapy.