Depth therapy shows large effects across studies, consistently producing benefits that increase even after therapy finishes.
For example, an analysis of multiple randomized controlled trials found an effect size of 0.97 for psychodynamic therapy. (In the standard benchmarks for effect size, 0.2 is considered small, 0.5 moderate and 0.8 large.) This effect size increased over time to 1.51 in follow-up assessments after therapy had ended.
Meta-analyses, which synthesize the findings from multiple studies, are the best way to assess the evidence base for psychodynamic therapy. Multiple meta-analyses have found that depth therapy is as effective as, if not more effective than cognitive behavior therapy and other evidence-based treatments.
Effectiveness of psychodynamic therapy
Here are three key meta-analyses which were conducted to investigate the effectiveness of psychodynamic, or depth therapy.
In this influential paper, Jonathan Shedler reviews multiple meta-analyses, comparing the efficacy of psychodynamic therapy to that of other therapies. The results indicate that psychodynamic therapy is as if not more effective than other evidence-based treatments, with effect sizes ranging from 0.78 to 1.46. For comparison, Shedler reports that effect sizes for medications for depression range from 0.17 to 0.31.
This meta-analysis compares psychodynamic therapy to other therapies, concluding that it is as efficacious. Christiane Steinert and colleagues use high methodological standards, controlling for researcher allegiance, applying the logic of equivalence testing "using one of the smallest margins ever suggested as compatible with equivalence," and using treatments established in efficacy as comparators.
This meta-analysis by Falk Leichsenring and colleagues examines psychodynamic therapy using a recently-updated model for assessing empirically supported treatments. From multiple randomized controlled trials they conclude that psychodynamic therapy demonstrates efficacy across several populations, and is an evidence-based treatment.
These meta-analyses, along with others published in the last couple of decades, have established psychodynamic therapy as an evidence-based therapy. They consistently find that depth therapy is not only effective in the short-term but also has lasting positive effects.
Perspectives from neuroscience
Additionally, studies drawing on brain research have offered support for the evidence basis of depth therapy. Here are a selection.
In this paper Mark Solms explores the neurobiological underpinnings of the core claims of psychoanalytic therapy—a type of psychodynamic or depth therapy. In particular he examines how much goes on outside of consciousness in the brain. So much that drives us occurs outside of the spotlight of our awareness. But things can be brought into consciousness to be transformed.
This study uses fMRI to examine changes in brain activity in depressed patients undergoing psychodynamic therapy. The researchers conclude that therapy led to changes in the brain's neural networks involved in self-referential processing and emotion regulation, providing evidence of the neurological impact of psychodynamic therapy.
This paper by prominent neuroscientists Robin Carhart-Harris and Karl Friston argues for the neurobiological basis of key Freudian concepts, particularly the dynamics in the relationship between normal waking consciousness—the ego—and the secondary, animistic or magical mode of thought found in dreaming and altered states of consciousness.
This paper examines Carl Jung's understanding of the unconscious, comparing the "recently evolved secondary consciousness associated with the default mode network and the human ego complex" with "a more archaic affect-based form of primary consciousness imbued with emotionally rich visual imagery." It examines these concepts in light of anthropology and the neuroscientific study of psychedelics.
Research into the effectiveness of depth, or psychodynamic, therapy, and the core concepts underlying the approach, has grown increasingly robust over the last few decades. The approach is at minimum on par with other evidence-based therapies—with the addition of having longer-lasting results, and arguably, being based on a more sophisticated and multi-layered understanding of the human mind.