# Investigation of Epistemic Equity in Urban Green Space and Mental Health Research: A Systematic Review

## TL;DR

This study reviews urban green space and mental health research to show that vulnerable groups are underrepresented, risking biased policies and mental health disparities.

## Contribution

The paper introduces the Equity Bias Framework to assess and address imbalances in research design, population sampling, and measurement methods.

## Key findings

- Most studies focus on healthy adults and self-report methods, limiting generalizability.
- Only 2.5% of research involves clinical populations, while 3.9% involves university students in experimental designs.
- Feasibility-driven research practices create a structurally biased knowledge base.

## Abstract

Public health relevance—How does this work relate to a public health issue?
Identifying who is represented and who is overlooked in green-space and mental-health research is essential for addressing inequities in mental health outcomes.Current evidence is shaped by feasibility-driven research practices that systematically exclude vulnerable groups, producing a structurally biased knowledge base.

Identifying who is represented and who is overlooked in green-space and mental-health research is essential for addressing inequities in mental health outcomes.

Current evidence is shaped by feasibility-driven research practices that systematically exclude vulnerable groups, producing a structurally biased knowledge base.

Public health significance—Why is this work of significance to public health?
This review quantitatively demonstrates the over-representation of convenience samples (healthy adults, university students) and the under-representation of clinical and age-vulnerable populations.Evidence is structurally concentrated in “cross-sectional × self-report × healthy adults” designs, limiting generalizability, inclusiveness, and clinical relevance of mental-health findings.

This review quantitatively demonstrates the over-representation of convenience samples (healthy adults, university students) and the under-representation of clinical and age-vulnerable populations.

Evidence is structurally concentrated in “cross-sectional × self-report × healthy adults” designs, limiting generalizability, inclusiveness, and clinical relevance of mental-health findings.

Public health implications—What are the key implications or messages for practitioners, policy makers and/or researchers in public health?
Reliance on feasibility-driven evidence risks perpetuating or worsening mental-health disparities through inequitable green-space policies.Equity oriented research, including clinical, age vulnerable and other underserved groups, with greater use of longitudinal and experimental designs, is needed to support inclusive and evidence-based public health and urban planning interventions.

Reliance on feasibility-driven evidence risks perpetuating or worsening mental-health disparities through inequitable green-space policies.

Equity oriented research, including clinical, age vulnerable and other underserved groups, with greater use of longitudinal and experimental designs, is needed to support inclusive and evidence-based public health and urban planning interventions.

Urban public green spaces are widely recognized for having positive effects on mental health, yet existing research shows imbalances in subjects and methodologies. Most studies examine healthy adults and self-reported indicators, giving limited attention to vulnerable populations; this may have led to a gap in evidence regarding “who is represented and who is overlooked.” This study systematically reviewed 235 empirical papers published in 2004–2024 following PRISMA 2020 to examine epistemic equity. The Equity Bias Framework was applied to operationalize epistemic equity by assessing imbalances in study design, psychometric measures, and population sampling. Results showed that the cross-sectional design, self-report, and community-dwelling adults combination accounted for the largest share (n = 99, 27.8%), whereas only 9 combinations in total (2.5%) involved clinical populations. The experimental design × self-report × university student patterns (n = 14, 3.9%) outnumber all experimental studies involving age-disadvantaged or clinical groups (n = 4, 1.1%). These patterns indicate that existing research evidence is shaped more by feasibility and accessibility than by representativeness and clinical relevance, raising concerns about epistemic equity. By introducing the Equity Bias Framework, this study provides a lens on current evidence and direction for research and policy promoting methodological diversity and sample inclusivity.