A visualized overview of systematic reviews and meta-analyses on low-carbon built environments: An evidence review map

Highlights

• Evidence syntheses for sustainable urban development are of increasing importance.

• An evidence map of systematic reviews and meta-analyses on this topic is presented.

• The map contains 131 reviews examining numerous aspects of built environment.

• The paper is supplemented by a free online database and interactive visual summaries.

Abstract

Sharing of key evidence on strategies for reducing resources consumption and lowering carbon footprint is essential to alleviating risks of increasing urbanization, population growth and looming climate change impacts. However, finding scientifically robust research and distilling knowledge to draw confident conclusions in a reasonable timeframe is challenging due to the sheer volume of rapidly accumulating research evidence. Primary evidence is aggregated in secondary studies, i.e. various types of reviews, including systematic reviews and meta-analyses. However, the number of secondary studies is also growing rapidly and their quality varies. This work presents the first systematic review of secondary studies which were claimed to be systematic reviews or meta-analyses of literature relevant to reducing carbon footprint of the built environment or its co-benefits (e.g., health and well-being). The resulting searchable and updatable database contains 131 reviews published between 2001 and early 2018. Importantly, the quality of the included reviews was assessed and categorized. The database is available via a dedicated website which includes interactive visualizations and filtering tools. In its current form, the interactive map and database can help discovery and appraisal of secondary evidence for decision-making and research use, supporting transition to low carbon future. This overview aimed to reveal trends and patterns, including gaps, in the publications of research syntheses relevant to sustainable built environment. The results showed that the number of reviews claiming to by systematic reviews or meta-analyses is rapidly increasing in recent years. However, the exact methodology used and the standard of adherence to methodological and reporting guidelines varies widely among reviews. The included reviews span different disciplines, such as environmental sciences, engineering, urban planning, public health, and social sciences. The first authors from USA, UK and Australia contributed the most relevant reviews. Health and well-being, along with closely related environment and nature, are currently the best synthesized subject areas, while there are still very few included reviews related to policy, economy or information technology, indicating synthesis gaps in these areas. Our analysis reveals the lack of standardized definitions of different types of research syntheses across disciplines, as well as poor reporting quality of research syntheses. We encourage detailed descriptions of methods, providing datasets and interactive visualizations as integral components of the future systematic reviews and evidence maps.

Introduction

The man-made built environment is associated with major crises related to energy, environment, climate change, poverty and vulnerability issues. It is the major consumer of energy, accounting for around 30–40% of the worldwide consumption, while it affects the environment in multiple ways by consuming resources and producing waste and pollution. It is also highly responsible for the global and local climate change via almost 39% of the greenhouse gas emissions (Abergel et al., 2018). The intense urbanization favours the development of the urban heat islands in densely packed cities, higher urban temperatures, increased energy consumption for cooling, lower indoor and outdoor thermal comfort levels and increased mortality and health risks for the vulnerable populations (Santamouris, 2014). Additionally, the built environment has to satisfy the needs for housing and infrastructures of the new and existing urban shelters as humanity is threatened by an unprecedented urbanization and population growth challenging the capacity of the planet and its climate (Santamouris, 2018).

Addressing challenges related to urbanisation and climate change involves answering a long list of specific questions and is very much associated with recent integrated and holistic research carried out in the built environment sector. Built environment research is interdisciplinary and involves many fields, such as urban planning, economics, law, engineering, public health and environmental sciences (McCormicket al., 2013, Romero-Lankaoet al., 2014). Different disciplines often take different approaches to address the issues of built environments, exemplified by architecture and engineering interventions (Smith, 2001, Vasilakopoulouet al., 2014), environmental psychology (Bechtel and Ts’erts’man, 2002, Gifford, 2007) and social science approaches (Moran, 2010, Wanden-Hannay, 2005). Therefore, there is complexity in integrating diverse fields of research, which also results in slow uptake of research-based evidence in this area. For example, in research relevant to the built environment, experiments equivalent to randomised controlled trials are often logistically challenging, costly and often impractical. As such, academics and practitioners are often limited to relay on observations, surveys or simulations (Frederiks et al., 2016, Pati, 2011). With rapidly growing number of primary studies, there is an increasing need to aggregate and summarise research-based evidence in a range of formats ranging from traditional narrative reviews to systematic reviews and meta-analyses (Hallet al., 2017, Kocet al., 2019).

Despite being originally developed to synthesize results of controlled experimental studies, systematic reviews and meta-analyses are gaining popularity as important tools for evidence synthesis in built environment. Systematic reviews usually follow protocols based on guidelines set out by acclaimed organisations such as Cochrane, the Campbell Collaboration and the Collaboration for Environmental Evidence. A systematic review approach accomplishes a transparent and rigorous summary of the current state of evidence and knowledge by collating primary (empirical) studies in the least biased manner. A systematic review can include a meta-analysis when quantitative synthesis is possible. It is notable that, if a meta-analysis does not follow a transparent and rigorous approach to collect and apprise the data from multiple studies, its conclusions may not be reliable.

Both systematic reviews and meta-analyses vary vastly in their quality (Ioannidis, 2016). Therefore, it is vital that the beneficiaries of the built environment research differentiate between high-quality systematic reviews and reviews that are less rigorous. Some researchers may still use the term ‘meta-analysis’ as synonymous with ‘systematic review’ (Chalmers et al., 2002). Even worse, the terms ‘systematic review’ and ‘meta-analysis’ are sometimes misused, when the reviews which do not use a systematic-review or meta-analytical approach bear the name of ‘systematic review’ and/or ‘meta-analysis’. Such confusion regarding the expectations on the quality, and mixed use of definitions of the reviews, calls for an urgent investigation of the state of research synthesis in the burgeoning field of sustainable built environments (Haddaway et al., 2017). To date, this field has no systematic overview of topics covered and methods used to perform systematic reviews and meta-analyses of literature. Our work aims to fill this gap.

Recently, a new method of aggregating secondary studies (i.e. reviews) has emerged, known as “evidence review mapping” (O’Leary et al., 2017). Using a transparent and rigorous approach modelled on an original systematic review approach, an evidence review map allows one to create a database of secondary studies (reviews) in a field. Such maps provide a snapshot or “bird’s eye view” of what has been done, in terms of synthesizing knowledge, rather than providing answer to any specific research or policy question. Evidence reviews maps do not directly measure the quantity or quality of the available primary evidence. However, by pointing to already existing syntheses they can direct researchers and policy makers to the underlying evidence. Thus, such maps are complementary to systematic reviews and systematic maps of original empirical studies (in fact, they are one level up in the synthesis hierarchy). Overall, evidence review maps have a range of benefits, including presenting and cataloguing research synthesis activity in a given field or on a given research topic, and locating gaps and gluts of evidence synthesis (i.e. areas where little or lots, respectively, reviews of a given type are available), enabling evidence-based decision-making and making research more efficient.

In this work, the main goal was to create a map of existing peer-reviewed systematic reviews and meta-analyses on the topic of low-carbon built environment. The resulting evidence review map achieves four additional aims. First, assessing the quality of the existing evidence syntheses and identifying areas for improvements. Second, locating gaps and clusters of research syntheses within low-carbon built environment research. Third, visualizing the temporal and geographical distributions of the included reviews. Finally, the evidence review map (i.e. database) is made accessible as a free, updatable and interactive web resource for researchers, practitioners, policymakers and members of the public. Thus, this work fosters best practice in research synthesis for the build environment, helps to raise awareness of what relevant syntheses has already been done, when and by whom. It also reveals potential shortcomings and existing overlaps, highlighting needs and opportunities for future effort in this increasingly important research area.