A Meta-Analysis of Sandplay Therapy Treatment Outcomes

Sandplay Enters the Evidence Base

Wiersma and colleagues’ 2022 meta-analysis marks a turning point for sandplay therapy’s institutional standing. For the first time, the scattered outcome studies that had accumulated over decades are synthesized into a single quantitative estimate of the modality’s effectiveness. The overall effect size — Hedges’ g = 0.62, a moderate-to-large effect — places sandplay in the same range as many treatments considered “evidence-based” by institutional standards. The numbers are not overwhelming, but they are robust and consistent: sandplay therapy produces measurable clinical improvement across diverse populations and conditions.

Strongest Where It Is Most Needed

The meta-analysis reveals a clinically significant pattern in sandplay’s differential effectiveness. The largest effect sizes appear for internalizing conditions — anxiety, depression, social withdrawal, trauma-related disturbance — while smaller effects appear for externalizing problems such as aggression, conduct difficulties, and hyperactivity. This pattern makes theoretical sense. Internalizing conditions involve the trapping of affect, memory, and meaning inside the psyche; sandplay’s therapeutic mechanism is precisely the externalization of this trapped material through three-dimensional symbolic composition. The patient who cannot speak their grief can place a figure alone in a desert of sand. The child who cannot name their fear can build a wall between a monster and a tiny human shape. The unconscious, given a physical medium, expresses what language has failed to carry. Externalizing conditions, by contrast, involve the discharge rather than the containment of affect, and sandplay’s contemplative, contained format may be less directly suited to their treatment.

The Measurement Problem

Wiersma is admirably forthright about the limitations of the existing literature. Many studies lack control groups, use heterogeneous outcome measures, and have small sample sizes. The meta-analysis works with what exists, but what exists is insufficient for the demands of contemporary evidence-based practice. This is not a criticism of sandplay but of the research infrastructure surrounding it. Sandplay therapy requires extensive training, specialized equipment, and a therapeutic relationship of sufficient duration and depth to permit the unconscious to reveal its patterns. These conditions are difficult to standardize, randomize, and manualize — the three operations that the RCT paradigm demands. The challenge for the sandplay community is to generate rigorous evidence without sacrificing the clinical qualities that make the modality therapeutically distinctive.

A Foundation for the Future

This meta-analysis provides the quantitative foundation that institutional gatekeepers require. It demonstrates that sandplay is not merely an experiential modality valued by its practitioners but a treatment with measurable outcomes and identifiable clinical indications. For Jungian clinicians, it is a tool for advocacy — evidence to present to insurers, training committees, and hospital administrators who demand numbers before they authorize resources. For the depth tradition more broadly, it is a reminder that the most imaginal and non-verbal forms of therapeutic engagement can withstand empirical scrutiny without losing their soul.