Synthesize a literature review from your sources

## 1. Current state of research Work on urban green space and adolescent mental health has moved from cross-sectional association to longitudinal designs, but the four sources supplied still measure exposure in three incompatible ways: distance to the nearest park (Study A), share of green cover within 500 m (Study B, Study D) and self-reported time outdoors (Study C). ## 2. Key themes and patterns - Small negative associations between green cover and self-reported internalising symptoms appear in Study A, Study B and Study D. - Effects are larger in denser neighbourhoods (Study B, Study D), suggesting exposure matters most where baseline access is lowest. - Only Study C measures use rather than availability, and it is the one study reporting no significant association. ## 3. Critical analysis of methodology Study A is cross-sectional and cannot separate selection from effect: families who value green space may already differ. Study B follows its cohort for two years but loses roughly a fifth of participants, and no attrition analysis is reported here. Study D adjusts for neighbourhood income, which Study A does not, so the two are not directly comparable. ## 4. Gaps and inconsistencies The availability-versus-use distinction is unresolved: no supplied source measures both. None reports effects by age band, although early and late adolescence differ sharply in independent mobility. ## 5. Synthesis Across these sources the defensible statement is narrow: greater residential green cover is associated with modestly lower internalising symptoms in dense urban settings, with the causal direction still open. ## 6. Future research A study measuring both availability and use in one cohort, stratified by age band, would resolve the central inconsistency above. Note: the sources you supplied report no effect size for Study C, so no pooled estimate is offered.