Background: Bradford Hill (BH) viewpoints are widely used to assess causality in systematic reviews, but their application has often lacked reproducibility. We describe an approach for assessing causality within systematic reviews (‘causal’ reviews), illustrating its application to the topic of income inequality and health. Our approach draws on principles of process tracing, a method used for case study research, to harness BH viewpoints to judge evidence for causal claims. Methods: In process tracing, a hypothesis may be confirmed by observing highly unique evidence and disconfirmed by observing highly definitive evidence. We drew on these principles to consider the value of finding supportive or contradictory evidence for each BH viewpoint characterised by its uniqueness and definitiveness.Results: In our exemplar systematic review, we hypothesised that income inequality adversely affects self-rated health and all-cause mortality. BH viewpoints ‘analogy’ and ‘coherence’ were excluded from the causal assessment because of their low uniqueness and low definitiveness. The ‘experiment’ viewpoint was considered highly unique and highly definitive, and thus could be particularly valuable. We propose five steps for using BH viewpoints in a ‘causal’ review: 1) define the hypothesis; 2) characterise each viewpoint; 3) specify the evidence expected for each BH viewpoint for a true or untrue hypothesis; 4) gather evidence for each viewpoint (e.g., systematic review meta-analyses, critical appraisal, background knowledge); 5) consider if each viewpoint was met (supportive evidence) or unmet (contradictory evidence).Conclusions: Incorporating process tracing has the potential to provide transparency and structure when using BH viewpoints in ‘causal’ reviews.

Context The economy has been long recognised as an important determinant of population health and a healthy population is considered important for economic prosperity. Aim To systematically review the evidence for a causal bidirectional relationship between aggregate economic activity (AEA) at national level for High Income Countries, and 1) population health (using mortality and life expectancy rates as indicators) and 2) inequalities in population health. Methods We undertook a systematic review of quantitative studies considering the relationship between AEA (GDP, GNI, GNP or recession) and population health (mortality or life expectancy) and inequalities for High Income Countries. We searched eight databases and grey literature. Study quality was assessed using an adapted version of the Effective Public Health Practice Project’s Quality Assessment tool. We used Gordis’ adaptation of the Bradford-Hill framework to assess causality. The studies were synthesised using Cochrane recommended alternative methods to meta-analysis and reported following the Synthesis without Meta-analysis (SWiM) guidelines. We assessed the certainty of the evidence base in line with GRADE principles. Findings Of 21,099 records screened, 51 articles were included in our analysis. There was no evidence for a consistent causal relationship (either beneficial or harmful) of changes in AEA leading to changes in population health (as indicated by mortality or life expectancy). There was evidence suggesting that better population health is causally related to greater AEA, but with low certainty. There was insufficient evidence to consider the causal impact of AEA on health inequalities or vice versa. Conclusions Changes in AEA in High Income Countries did not have a consistently beneficial or harmful causal relationship with health, suggesting that impacts observed may be contextually contingent. We tentatively suggest that improving population health might be important for economic prosperity. Whether or not AEA and health inequalities are causally linked is yet to be established.

Policy Points Income is thought to impact a broad range of health outcomes. However, whether income inequality (how unequal the distribution of income is in a population) has an additional impact on health is extensively debated. Studies that use multilevel data, which have recently increased in popularity, are necessary to separate the contextual effects of income inequality on health from the effects of individual income on health. Our systematic review found only small associations between income inequality and poor self-rated health and all-cause mortality. The available evidence does not suggest causality, although it remains methodologically flawed and limited, with very few studies using natural experimental approaches or examining income inequality at the national level.ContextWhether income inequality has a direct effect on health or is only associated because of the effect of individual income has long been debated. We aimed to understand the association between income inequality and self-rated health (SRH) and all-cause mortality (mortality) and assess if these relationships are likely to be causal.MethodsWe searched Medline, ISI Web of Science, Embase, and EconLit (PROSPERO: CRD42021252791) for studies considering income inequality and SRH or mortality using multilevel data and adjusting for individual-level socioeconomic position. We calculated pooled odds ratios (ORs) for poor SRH and relative risk ratios (RRs) for mortality from random-effects meta-analyses. We critically appraised included studies using the Risk of Bias in Nonrandomized Studies - of Interventions tool. We assessed certainty of evidence using the Grading of Recommendations Assessment, Development and Evaluation framework and causality using Bradford Hill (BH) viewpoints.FindingsThe primary meta-analyses included 2,916,576 participants in 38 cross-sectional studies assessing SRH and 10,727,470 participants in 14 cohort studies of mortality. Per 0.05-unit increase in the Gini coefficient, a measure of income inequality, the ORs and RRs (95% confidence intervals) for SRH and mortality were 1.06 (1.03-1.08) and 1.02 (1.00-1.04), respectively. A total of 63.2% of SRH and 50.0% of mortality studies were at serious risk of bias (RoB), resulting in very low and low certainty ratings, respectively. For SRH and mortality, we did not identify relevant evidence to assess the specificity or, for SRH only, the experiment BH viewpoints; evidence for strength of association and dose-response gradient was inconclusive because of the high RoB; we found evidence in support of temporality and plausibility.ConclusionsIncreased income inequality is only marginally associated with SRH and mortality, but the current evidence base is too methodologically limited to support a causal relationship. To address the gaps we identified, future research should focus on income inequality measured at the national level and addressing confounding with natural experiment approaches.

In recent decades, 'whole school' approaches to improving health have gained traction, based on settings-based health promotion understandings which view a setting, its actors and processes as an integrated 'whole' system with multiple intervention opportunities. Much less is known about 'whole institution' approaches to improving health in tertiary education settings. We conducted a scoping review to describe both empirical and non-empirical (e.g. websites) publications relating to 'whole settings', 'complex systems' and 'participatory'/'action' approaches to improving the health of students and staff within tertiary education settings. English-language publications were identified by searching five academic and four grey literature databases and via the reference lists of studies read for eligibility. We identified 101 publications with marked UK overrepresentation. Since the 1970s, publications have increased, spanning a gradual shift in focus from 'aspirational' to 'conceptual' to 'evaluative'. Terminology is geographically siloed (e.g., 'healthy university' (UK), 'healthy campus' (USA)). Publications tend to focus on 'health' generally rather than specific health dimensions (e.g. diet). Policies, arguably crucial for cascading systemic change, were not the most frequently implemented intervention elements. We conclude that, despite the field's evolution, key questions (e.g., insights into who needs to do what, with whom, where and when; or efficacy) remain unanswered.

This systematic review synthesised evidence on associations between nature-based early childhood education (ECE) and children’s social, emotional, and cognitive development. A search of nine databases was concluded in August 2020. Studies were eligible if: (a) children (2–7 years) attended ECE, (b) ECE integrated nature, and (c) assessed child-level outcomes. Two reviewers independently screened full-text articles and assessed study quality. Synthesis included effect direction, thematic analysis, and results-based convergent synthesis. One thousand three hundred and seventy full-text articles were screened, and 36 (26 quantitative; 9 qualitative; 1 mixed-methods) studies were eligible. Quantitative outcomes were cognitive (n = 11), social and emotional (n = 13), nature connectedness (n = 9), and play (n = 10). Studies included controlled (n = 6)/uncontrolled (n = 6) before-after, and cross-sectional (n = 15) designs. Based on very low certainty of the evidence, there were positive associations between nature-based ECE and self-regulation, social skills, social and emotional development, nature relatedness, awareness of nature, and play interaction. Inconsistent associations were found for attention, attachment, initiative, environmentally responsible behaviour, and play disruption/disconnection. Qualitative studies (n = 10) noted that nature-based ECE afforded opportunities for play, socialising, and creativity. Nature-based ECE may improve some childhood development outcomes, however, high-quality experimental designs describing the dose and quality of nature are needed to explore the hypothesised pathways connecting nature-based ECE to childhood development (Systematic Review Registration: CRD42019152582).

Background Lower incomes are associated with poorer mental health and wellbeing, but the extent to which income has a causal effect is debated. We aimed to synthesise evidence from studies measuring the impact of changes in individual and household income on mental health and wellbeing outcomes in working-age adults (aged 16-64 years). Methods For this systematic review and meta-analysis, we searched MEDLINE, Embase, Web of Science, PsycINFO, ASSIA, EconLit, and RePEc on Feb 5, 2020, for randomised controlled trials (RCTs) and quantitative non-randomised studies. We had no date limits for our search. We included English-language studies measuring effects of individual or household income change on any mental health or wellbeing outcome. We used Cochrane risk of bias (RoB) tools. We conducted three-level random-effects meta-analyses, and explored heterogeneity using meta-regression and stratified analyses. Synthesis without meta-analysis was based on effect direction. Critical RoB studies were excluded from primary analyses. Certainty of evidence was assessed using Grading of Recommendations Assessment, Development and Evaluation (GRADE). This study is registered with PROSPERO, CRD42020168379. Findings Of 16 521 citations screened, 136 were narratively synthesised (12.5% RCTs) and 86 meta-analysed. RoB was high: 30.1% were rated critical and 47.1% serious or high. A binary income increase lifting individuals out of poverty was associated with 0.13 SD improvement in mental health measures (95% CI 0.07 to 0.20; n=42 128; 18 studies), considerably larger than other income increases (0.01 SD improvement, 0.002 to 0.019; n=216 509, 14 studies). For wellbeing, increases out of poverty were associated with 0.38 SD improvement (0.09 to 0.66; n=101 350, 8 studies) versus 0.16 for other income increases (0.07 to 0.25; n=62 619, 11 studies). Income decreases from any source were associated with 0.21 SD worsening of mental health measures (-0.30 to -0.13; n=227 804, 11 studies). Effect sizes were larger in low-income and middle-income settings and in higher RoB studies. Heterogeneity was high (I-2=79-87%). GRADE certainty was low or very low. Interpretation Income changes probably impact mental health, particularly where they move individuals out of poverty, although effect sizes are modest and certainty low. Effects are larger for wellbeing outcomes, and potentially for income losses. To best support population mental health, welfare policies need to reach the most socioeconomically disadvantaged. Copyright (C) 2022 The Author(s). Published by Elsevier Ltd.

Background: Income inequality has been linked to health and mortality. While there has been extensive research exploring the relationship, the evidence for whether the relationship is causal remains disputed. We describe the methods for a systematic review that will transparently assess whether a causal relationship exists between income inequality and mortality and self-rated health. Methods: We will identify relevant studies using search terms relating to income inequality, mortality, and self-rated health (SRH). Four databases will be searched: MEDLINE, ISI Web of Science, EMBASE, and the National Bureau of Economic Research. The inclusion criteria have been developed to identify the study designs best suited to assess causality: multilevel studies that have conditioned upon individual income (or a comparable measure, such as socioeconomic position) and natural experiment studies. Risk of bias assessment of included studies will be conducted using ROBINS-I. Where possible, we will convert all measures of income inequality into Gini coefficients and standardize the effect estimate of income inequality on mortality/SRH. We will conduct random-effects meta-analysis to estimate pooled effect estimates when possible. We will assess causality using modified Bradford Hill viewpoints and assess certainty using GRADE. Discussion: This systematic review protocol lays out the complexity of the relationship between income inequality and individual health, as well as our approach for assessing causality. Understanding whether income inequality impacts the health of individuals within a population has major policy implications. By setting out our methods and approach as transparently as we can, we hope this systematic review can provide clarity to an important topic for public policy and public health, as well as acting as an exemplar for other "causal reviews".

BACKGROUND The purpose was to synthesize evidence on the association between nature-based Early Childhood Education (ECE) and children's physical activity (PA) and motor competence (MC). METHODS A literature search of 9 databases was concluded in August 2020. Studies were eligible if (1) children were aged 2-7 years old and attending ECE, (2) ECE settings integrated nature, and (3) assessed physical outcomes. Two reviewers independently screened full-text articles and assessed study quality. Synthesis was conducted using effect direction (quantitative), thematic analysis (qualitative), and combined using a results-based convergent synthesis. RESULTS 1370 full-text articles were screened and 39 (31 quantitative and 8 qualitative) studies were eligible; 20 quantitative studies assessed PA and 6 assessed MC. Findings indicated inconsistent associations between nature-based ECE and increased moderate to vigorous PA, and improved speed/agility and object control skills. There were positive associations between nature-based ECE and reduced sedentary time and improved balance. From the qualitative analysis, nature-based ECE affords higher intensity PA and risky play, which could improve some MC domains. The quality of 28/31 studies was weak. CONCLUSIONS More controlled experimental designs that describe the dose and quality of nature are needed to better inform the effectiveness of nature-based ECE on PA and MC.

In fields (such as population health) where randomised trials are often lacking, systematic reviews (SRs) can harness diversity in study design, settings and populations to assess the evidence for a putative causal relationship. SRs may incorporate causal assessment approaches (CAAs), sometimes called 'causal reviews', but there is currently no consensus on how these should be conducted. We conducted a methodological review of self-identifying 'causal reviews' within the field of population health to establish: (1) which CAAs are used; (2) differences in how CAAs are implemented; (3) how methods were modified to incorporate causal assessment in SRs. Three databases were searched and two independent reviewers selected reviews for inclusion. Data were extracted using a standardised form and summarised using tabulation and narratively. Fifty-three reviews incorporated CAAs: 46/53 applied Bradford Hill (BH) viewpoints/criteria, with the remainder taking alternative approaches: Medical Research Council guidance on natural experiments (2/53, 3.8%); realist reviews (2/53, 3.8%); horizontal SRs (1/53, 1.9%); 'sign test' of causal mechanisms (1/53, 1.9%); and a causal cascade model (1/53, 1.9%). Though most SRs incorporated BH, there was variation in application and transparency. There was considerable overlap across the CAAs, with a trade-off between breadth (BH viewpoints considered a greater range of causal characteristics) and depth (many alternative CAAs focused on one viewpoint). Improved transparency in the implementation of CAA in SRs in needed to ensure their validity and allow robust assessments of causality within evidence synthesis.

The 'inclusion health' agenda aims to draw attention to health disadvantages accompanying experiences putatively characterised by social exclusion, such as homelessness, problem substance use, or imprisonment. However, its increasing prominence has surfaced conceptual uncertainties and potential tensions with other understandings of health inequalities. We undertook a discourse analysis of how recent health inequalities policy documents describe, explain, and make recommendations relating to inclusion health. Using the UK as a case study, and with reference to public health accounts of multi-level governance theory, we selected five recent health inequalities policy reviews covering Scotland, UK, European Union, and the World Health Organisation. All documents referred to some inclusion health concerns, though their relative emphasis differed between documents. Terms like inclusion, exclusion, and vulnerability were commonly used, but ill-defined and often ambiguous. Explanatory discourses were diverse, with a particular focus on intergenerational cycles and disproportionate exposure to risk, with a varying emphasis on individual versus structural factors. Few documents provided coherent explanatory accounts for the relationship between the issues of interest to inclusion health, their associations with poor health, and other axes of inequality. Our results suggest that health inequalities policymaking in a multi-level context may benefit from comprehensive conceptual frameworks which encompass diverse forms of social stratification, advantage, and disadvantage, and acknowledge potential tensions and trade-offs between different understandings. This may necessitate further theoretical and empirical work for inclusion health on its definitions, bounds, and how its scope of interest interacts with other forms of social and health inequality.

BACKGROUND AND OBJECTIVE:This article explores the need for conceptual advances and practical guidance in the application of the GRADE approach within public health contexts. METHODS:We convened an expert workshop and conducted a scoping review to identify challenges experienced by GRADE users in public health contexts. We developed this concept article through thematic analysis and an iterative process of consultation and discussion conducted with members electronically and at three GRADE Working Group meetings. RESULTS:Five priority issues can pose challenges for public health guideline developers and systematic reviewers when applying GRADE: (1) incorporating the perspectives of diverse stakeholders; (2) selecting and prioritizing health and "nonhealth" outcomes; (3) interpreting outcomes and identifying a threshold for decision-making; (4) assessing certainty of evidence from diverse sources, including nonrandomized studies; and (5) addressing implications for decision makers, including concerns about conditional recommendations. We illustrate these challenges with examples from public health guidelines and systematic reviews, identifying gaps where conceptual advances may facilitate the consistent application or further development of the methodology and provide solutions. CONCLUSION:The GRADE Public Health Group will respond to these challenges with solutions that are coherent with existing guidance and can be consistently implemented across public health decision-making contexts.

Effect direction (evidence to indicate improvement, deterioration, or no change in an outcome) can be used as a standardized metric which enables the synthesis of diverse effect measures in systematic reviews. The effect direction (ED) plot was developed to support the synthesis and visualization of effect direction data. Methods for the ED plot require updating in light of new Cochrane guidance on alternative synthesis methods. To update the ED plot, statistical significance was removed from the algorithm for within-study synthesis and use of a sign test was considered to examine whether patterns of ED across studies could be due to chance alone. The revised methods were applied to an existing Cochrane review of the health impacts of housing improvements. The revised ED plot provides a method of data visualization in synthesis without meta-analysis that incorporates information about study characteristics and study quality, using ED as a common metric, without relying on statistical significance to combine outcomes of single studies. The results of sign tests, when appropriate, suggest caution in over-interpreting apparent patterns in effect direction, especially when the number of included studies is small. The revised ED plot meets the need for alternative methods of synthesis and data visualization when meta-analysis is not possible, enabling a transparent link between the data and conclusions of a systematic review. ED plots may be particularly useful in reviews that incorporate nonrandomized studies, complex systems approaches, and diverse sources of evidence, due to the variety of study designs and outcomes in such reviews.

Background Lower incomes are associated with poorer mental health (MH) and wellbeing, but the extent to which income has a causal effect (rather than reflecting reverse causation or confounding factors such as education) is debated. We synthesised evidence from studies measuring the impact of changes in individual or household incomes on MH and wellbeing for working-age adults (16–64 years). Methods We searched MEDLINE, Embase, Web of Science, PsycINFO, ASSIA, EconLit and RePEc for randomised controlled trials (RCTs) and quantitative non-randomised studies (NRSs) – PROSPERO registration CRD42020168379. We included studies measuring effects of income change on any MH or wellbeing outcome. Screening and risk of bias (RoB) assessment were completed independently by two reviewers, using ROBINS-I for NRSs and RoB-2 for RCTs. As per Cochrane guidance, we conducted narrative synthesis based on direction of effects (benefit vs harm) for relevant datapoint(s) within each included study, and compared findings by RoB. Meta-analysis is in progress. Results Of 16,521 hits screened, 17 RCTs and 118 NRSs (67.0% longitudinal) were included. Most studies were from high-income settings (71.9%), with 26.7% from USA. RoB was high: 102 studies (75.6%) were rated serious/critical, with confounding being the highest-rated RoB domain in 81.1% of these studies. Where known (53.7% of studies), the most common income sources studied were cash transfers (20.2%), natural disasters/welfare policy changes (7.5%) and lottery wins (5.2%). For mental health, 80.4% of 112 datapoints reported beneficial effects of income (95%CI 73.0–87.7%, sign test p Conclusion Income increases are linked to improved MH and wellbeing, but on preliminary synthesis effect sizes appear small in the most robust studies. Income provision alone may not be adequate to improve mental health – given that more generous welfare policies are known to be linked with better population MH, it is possible other elements such as conditionality or financial security are also important.

Background: Regression discontinuity designs are non-randomized study designs that permit strong causal inference with relatively weak assumptions. Interest in these designs is growing but there is limited knowledge of the extent of their application in health. We aimed to conduct a comprehensive systematic review of the use of regression discontinuity designs in health research. Methods: We included studies that used regression discontinuity designs to investigate the physical or mental health outcomes of any interventions or exposures in any populations. We searched 32 health, social science, and gray literature databases (1 January 1960 to 1 January 2019). We critically appraised studies using eight criteria adapted from the What Works Clearinghouse Standards for regression discontinuity designs. We conducted a narrative synthesis, analyzing the forcing variables and threshold rules used in each study. Results: The literature search retrieved 7658 records, producing 325 studies that met the inclusion criteria. A broad range of health topics was represented. The forcing variables used to implement the design were age, socioeconomic measures, date or time of exposure or implementation, environmental measures such as air quality, geographic location, and clinical measures that act as a threshold for treatment. Twelve percent of the studies fully met the eight quality appraisal criteria. Fifteen percent of studies reported a prespecified primary outcome or study protocol. Conclusions: This systematic review demonstrates that regression discontinuity designs have been widely applied in health research and could be used more widely still. Shortcomings in study quality and reporting suggest that the potential benefits of this method have not yet been fully realized.

BackgroundIncome is thought to be a major determinant of mental health, but we believe this literature has not been quantitatively synthesised in its entirety. We systematically reviewed studies assessing the effect of income changes on mental health in working-age adults (16–64 years).MethodsWe searched seven databases (MEDLINE, Embase, Web of Science, PsycINFO, ASSIA, EconLit, and RePEc) for randomised controlled trials and quantitative non-randomised studies with no date limits on Feb 5, 2020 (PROSPERO CRD42020168379). We included English-language studies measuring effects of individual or household income change on any mental health or wellbeing outcome (search terms included mental health, depression, anxiety, wellbeing, quality of life, life satisfaction, psychological distress AND income [or synonym] NEAR change [or synonym]). Risk of bias was assessed using Cochrane methods. We did three-level, random-effects, meta-analyses and explored potential effect modification using meta-regression and stratified analyses. Critical risk of bias studies were excluded from primary analyses.FindingsOf 16 521 hits screened, 136 studies (12·5% randomised controlled trials) were narratively synthesised and 86 meta-analysed. Risk of bias was high, with 41 studies (30·1%) rated critical and 64 (47·1%) serious or high. The source of income change was generally not known (n=63, 46·3% of studies), with welfare policies (n=38, 28·0%), natural disasters (n=10, 7·4%), and lottery wins (n=7, 5·1%) being the most commonly described sources. A binary income increase was associated with 0·08 SD improvement in mental health (95% CI 0·038 to 0·13; n=258 637) and an income decrease with 0·21 SD worsening (–0·30 to –0·13; n=227 804). For continuous log(income) exposures, a 10% income increase was associated with 0·003 SD improvement in mental health (0·000 to 0·005; n=1 510 221). For wellbeing, binary increases were associated with 0·27 SD improvement (0·14 to 0·41; n=163 969) and a 10% income increase with 0·003 SD improvement (0·002 to 0·005; n=105 326). Heterogeneity was high (I2=79–87%). Effect sizes were larger in low-income and middle-income settings, for people of lower socioeconomic position, and in studies with higher risk of bias.InterpretationEffects are potentially larger for wellbeing outcomes, for income losses, and in the most socioeconomically disadvantaged. To support mental health, welfare policies need to reach the most disadvantaged, and consider wider factors such as financial insecurity and employment.FundingWellcome Trust (218105/Z/19/Z and 205412/Z/16/Z), National Health Service Research Scotland (SCAF/15/02), Medical Research Council (MC_UU_00022/2), and Chief Scientist Office (SPHSU17).

Welfare to work interventions seek to move out-of-work individuals from claiming unemployment benefits towards paid work. However, previous research has highlighted that for over-50s, particularly those with chronic health conditions, participation in such activities are less likely to result in a return to work. Using longitudinal semi-structured interviews, we followed 26 over-50s during their experience of a mandated welfare to work intervention (the Work Programme) in the United Kingdom. Focusing on their perception of suitability, we utilise and adapt Candidacy Theory to explore how previous experiences of work, health, and interaction with staff (both in the intervention, and with healthcare practitioners) influence these perceptions. Despite many participants acknowledging the benefit of work, many described a pessimism regarding their own ability to return to work in the future, and therefore their lack of suitability for this intervention. This was particularly felt by those with chronic health conditions, who reflected on difficulties with managing their conditions (e.g., attending appointments, adhering to treatment regimens). By adapting Candidacy Theory, we highlighted the ways that mandatory intervention was navigated by all the participants, and how some discussed attempts to remove themselves from this intervention. We also discuss the role played by decision makers such as employment-support staff and healthcare practitioners in supporting or contesting these feelings. Findings suggest that greater effort is required by policy makers to understand the lived experience of chronic illness in terms of ability to RTW, and the importance of inter-agency work in shaping perceptions of those involved.

In-premise marketing is commonly used to promote foods that are high in fat, sugar or salt. In order to inform development of public policy in this area, this systematic review sought to determine the quantity and quality of English-language evidence which examines the role and impact of in-premise advertising (e.g., signage, posters) and positional promotions (e.g., checkout displays) on consumer behaviour and diet-related outcomes in retail, out-of-home (i.e., cafes, restaurants, takeaways) and online purchasing environments. Sixty-two studies met inclusion criteria, of which 69% (n=42) were identified as being methodologically weak. The best-available evidence constitutes findings from four methodologically strong studies, and ten moderate studies which are not confounded by additional promotions such as price or availability. These studies predominantly found evidence that in-premise marketing is likely to be successful in influencing consumer behaviour towards targeted items, across retail and out-of-home settings. These findings provide a basis for authorities to consider acting to restrict in-premise marketing of unhealthy foods and encouraging the in-premise marketing of healthier products. This review identified gaps in the evidence available on non-sales outcomes, and on online purchase environments. These gaps, and identified methodological limitations of the extant evidence remain to be addressed by future research.

Abstract Background Several systematic reviews have reviewed the evidence relating to nature on aspects of children and adolescent’s health and wellbeing; however, none have looked at the associations or effectiveness of attending nature-based early childhood education (ECE). The main objective is to systematically review and synthesise the evidence to determine if nature-based ECE enhances children’s health, wellbeing and development. Methods We will search the following electronic databases (from inception onwards): MEDLINE, Scopus, PsycINFO, ERIC, SportDiscus, Australian Education Index, British Education Index, Child Development and Adolescent studies, and Applied Social Sciences Index and Abstracts. Grey literature will be identified searching dissertations and reports (e.g. Open Grey, Dissertations Theses Database [ProQuest], and Google Scholar). All types of studies (quantitative and qualitative) conducted in children (aged 2–7 years old) attending ECE who had not started education at primary or elementary school will be included. The exposure of interest will be nature-based ECE settings that integrate nature into their philosophy and/or curriculum and environment. The outcomes of interest will be all aspects of the child’s physical, cognitive, social and emotional health wellbeing and development. Two reviewers will independently screen full-text articles. The study methodological quality (or bias) will be appraised using appropriate tools. If feasible, a meta-analysis will be conducted using a random-effect model for studies similar in exposure and outcome. Where studies cannot be included in a meta-analysis, findings will be summarised based on the effect directions and a thematic analysis will be conducted for qualitative studies. Discussion This systematic review will capture the state of the current literature on nature-based ECE for child health, wellbeing and development. The results of this study will be of interest to multiple audiences (including researchers and policy makers). Results will be published in a peer-reviewed journal. Gaps for future research will be identified and discussed. Systematic review registration PROSPERO CRD42019152582