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Big Data Reality Check (BDRC) for public health: to what extent the environmental health and health services research did meet the ‘V’ criteria for big data? A study protocol

Introduction Big data technologies have been talked up in the fields of science and medicine. The V-criteria (volume, variety, velocity and veracity, etc) for defining big data have been well-known and even quoted in most research articles; however, big data research into public health is often misrepresented due to certain common misconceptions. Such misrepresentations and misconceptions would mislead study designs, research findings and healthcare decision-making. This study aims to identify the V-eligibility of big data studies and their technologies applied to environmental health and health services research that explicitly claim to be big data studies. Methods and analysis Our protocol follows Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P). Scoping review and/or systematic review will be conducted. The results will be reported using PRISMA for Scoping Reviews (PRISMA-ScR), or PRISMA 2020 and Synthesis Without Meta-analysis guideline. Web of Science, PubMed, Medline and ProQuest Central will be searched for the articles from the database inception to 2021. Two reviewers will independently select eligible studies and extract specified data. The numeric data will be analysed with R statistical software. The text data will be analysed with NVivo wherever applicable. Ethics and dissemination This study will review the literature of big data research related to both environmental health and health services. Ethics approval is not required as all data are publicly available and involves confidential personal data. We will disseminate our findings in a peer-reviewed journal. PROSPERO registration number CRD42021202306.


INTRODUCTION Environment affects human health
The quality of the environment is a powerful determinant of human health. Environmental health refers to the influence of environmental factors on human health. 1 2 The environmental factors that are attributable to diseases of high global burden have been classified into physical, chemical, biological, social and other factors. 3 Recent studies reported that 23% of deaths between 2006 and 2016 were attributable to environmental causes. 4 5 Environmental health once focused on the prevention of infectious diseases; however, the focus has shifted toward chronic diseases such as cardiovascular diseases. 6 The WHO estimated that ischaemic heart disease is the biggest killer worldwide (16% of total deaths) in 2019. 7 The reduction of environmental risks such as PM2.5 levels in the air was associated with decreases in cardiovascular mortality. 8 Although the US Environmental Protection Agency was established in the 1970s and aimed to manage air, water and soil pollution control and remediation, air pollution continues to be the largest environmental health risk to public health in the US. 9 The simple statistical learning methods to study the linkage of environmental health risk factors and potential diseases have been replaced by the big data analysis methods, which improves the accuracy of evaluation, evolves our understanding of the relationship between environmental and human health, and enhances public health policies that Strengths and limitations of this study ► This study is the first one to assess the V-eligibility of public health studies for big data research, particularly in environmental health and health services research. ► It highlights the characteristics of V-eligible big data research and promotes the proper use of big data in environmental health and health services research. ► Some research articles could be too obscure in reporting their V-eligibility. ► Some researchers might not respond to our email queries and online questionnaire survey to clarify and verify information.
Open access reduce populations at risk. For example, since previous studies demonstrated that reduction in air pollution exposure can improve respiratory health, a recent study used a deep neural network method to identify the environmental health risk factors of acute respiratory diseases. 10 Additionally, a recent study launched a national long-term birth cohort study that aimed to use big data to investigate environmental influences on children's health and address the need for public health strategies to reduce the burden of environment-related diseases. 11 Health services in public health The implementation of health services focuses on individuals, and the target of public health is the health condition of the overall population. 12-15 Offering health services inside or outside the clinical stage to the population is a critical strategy for developing and maintaining public health. 15 Health services need to be sufficiently available, high-quality, cost-affordable, and accessible. [16][17][18] Both health services and public health strive to prevent and intervene against acute diseases, chronic diseases, injuries, and risks. 12 Diverse health services (eg, data monitoring, primary healthcare, illness screening, injury protection, drug development, and health promotion) and professional personnel collaboratively benefit the health of the public, and the public health services system plays an irreplaceable role in the management of individual health. 12 16 19 Data regarding incidence, morbidity, prevalence, mortality, and rate of recovery that are obtained from the health services system not only inform the data monitoring and surveillance in epidemiology, but also serve as references for the development of health promotion policies and strategies. 14 The construction of sufficient and efficient health services is necessary for response and recovery during public health emergencies. 18 What is big data? The term big data was first used at Silicon Graphics in the mid-1990s according to Diebold,20 Cox et al 21 first used big data in publications on data-intensive computing in 1997. The term big data was defined in various ways in recent publications. Laney 22 highlighted three dimensions (volume, velocity, and variety) of big data in a research note in 2001. Moreover, De Mauro et al 23 characterised big data as high volume, high velocity, and high variety (the 3Vs criteria). Specially designed technologies and analytics are required to transform such data into valuable information.
Use of big data in environmental health research Data-intensive research in environmental health has grown, 24 especially over the last two decades. 25 These studies require large datasets. For instance, studies on air pollution 26 have processed terabytes of data to identify air pollution as the largest killer worldwide. 27 Meanwhile, deaths due to chemical pollution and soil pollution have also been increasing. 28 Studies on mobile health would require several gigabytes of GPS data. 29 As big data became a buzzword in public health research, some researchers may not aware of or did not follow its definitions. It is not uncommon for non-trivial datasets to be called big data. As a result, non-V-eligible (zero V) big data research on environmental health exists that could mislead healthcare decision-makers. This is the first study that seeks to identify the V-eligibility of big data studies and their technologies applied to environmental health research. It is anticipated that the findings will promote V-eligible big data research on environmental health.
Use of big data in health services research Big data and its technologies change rapidly and improve the efficiency of various data workflows, such as data collection, processing, utilisation, and management in health services; examples include electronic health records (EHR), digital health applications, research studies, and so on. [30][31][32][33][34] Based on a preliminary search that was conducted in the Web of Science (WOS), 34% of all published big data research in public-health-related categories (ie, primary healthcare, public, environmental and occupational health, healthcare sciences and services, health policy and services) covered health services. Developing big data technologies and architectures such as Internet of Things (IoT) based patient monitoring system, 35 which facilitate the continued exploration of health services such as the performance of operations, development of personalised medicine, evaluation of policies, reduction of medical expenses, 36 disease prevention, enhancement of overall service capacity and communication among service providers, mediators and receivers. 36 37 Recent research [38][39][40][41] identified the major challenges of big data including data structure, data security, data standardisation, data storage and transfer, and training of data analysts. For example, data management in health services was hindered by difficulties in sharing EHRs due to slow standardisation, non-compliance with standards, and a lack of expertise. In addition, big data is not easy to manage using traditional database technology designed for well-structured data. Moreover, enabling artificial intelligence investigations into big data analytics would require even better technologies. 30 42 Big data have outgrown traditional data technologies Big data analytics, like that for traditional data, aims to generate information from data but with different technologies. 43 Even if parts of big data were stored in traditional databases, yet multiple sources and fast growth of such data (eg, from the web, social networks, sensor networks, scientific experiments and others) in terms of types, sizes, timeliness, and complexity would require big data analytics. 44 45 Integrating various forms of data, that is, structured, semi-structured, and unstructured data, would also require big data analytics, 46 rather than the ordinary Structured Query Language designed for managing relational databases. 43 Therefore, data-intensive computing tools, for example, Hadoop and Spark, are commonly used for dig data processing. 45 There have been unstructured data management systems for healthcare data; for example, Luo et al 47 developed a double-reading/entry system for extracting key-value data items (ie, structured data) from the unstructured medical records (ie, texts, drawings, laboratory test results and physicians' notes) and for curating semi-structured EHR databases.
The V-criteria for big data What makes big data different from ordinary data? The main differences lie in the so-called 'V' characteristics of big data. 43 Laney originally suggested that volume, variety, and velocity are the three basic 'Vs' that characterise big data, as originally suggested by META Group. 22 Then big data's characteristics surpassed the 3Vs. Yin et al 48 stated that volume, variety, velocity, veracity, and value are the 5Vs of big data. Andreu-Perez et al 49 stated that volume, variety, velocity, veracity, value, and variability are the 6Vs that are applicable to health data research. Among these characteristics, volume, variety, velocity, and veracity constitute the most popular criteria for big data. 50 51 Therefore, these 4Vs criteria (table 1) were adopted in this review.
Volume, or the magnitude of data generated every second, describes how big the datasets are. 52 The size of big data should span terabytes and petabytes. 53 54 There have already been data that exceed zettabytes, and the data sizes are expected to increase 20-fold within the next 10 years. 48 Nevertheless, the size alone does not define big data. 49 Variety or the structural heterogeneity of a dataset, refers to the coexistence of various types of data (ie, structured, semi-structured, and unstructured data). [44][45][46] In contrast to tabular data and other well-structured data, 52 images, audio, and videos are unstructured data that require customised analysis. 55 Extensible Markup Language and JavaScript Object Notation are useful techniques for managing semi-structured data. 56 Velocity refers to the speed and rate at which data are generated and analysed to create, capture, process and store data. 53 Given the rapid growth of data integration, a real-time processing solution is needed. A data stream is an unbounded sequence of event processing in real time or near real time. 56 In environmental health research, real-time streams are commonly used in distributed and remote sensing techniques. 3 26 55 Veracity, or the trustworthiness of the data, refers to the reliability and provenance of the data. 50 For obvious reasons such as the sheer volume of data, big data must be cleaned and harmonised in an automated manner. 53 Kitchin et al 57 found that few environmental health datasets fulfilled the 3Vs (ie, very large volume, fast and continuous velocity, and wide variety). Some datasets, such as sensors for pollution and sound, only produce gigabytes of data per year. In addition, insufficient data quality, precision, and timeliness of the IoT-generated big IoT data presented challenges to the processing of big data. 58 Although social sensing has widespread usage in mobile devices, its reliability (ie, veracity) still requires slow human verification. 59 Big data research in medicine is often misrepresented Traditional IT approaches to data management are no longer suitable for managing large unstructured data and processing data-intensive tasks. 60 For example, Excel and SPSS were not designed for handling big data 61 but are often used in non-V-eligible big data research as the main (if not only) data management and processing tools. Common visualisation software (eg, Pajek and Cytoscape for visualisation of the social/biological networks of above-average sizes) was not designed for big data, but were often mislabelled in non-V-eligible research as big data tools. Genuine big data research requires special data engineering to facilitate the acquisition, access, processing, analysis, mining, modelling, and so on. 62 In particular, ensemble analysis, association analysis, highdimensional analysis, deep analysis, precision analysis, and divide-and-conquer analysis have been proposed as the six major strategies and technologies that enable big data research. 63 Objectives This study aims to identify the V-eligibility of big data studies on and their technologies applied to environmental health and health services research that explicitly claimed to be big data studies.

This protocol follows Preferred Reporting Items for
Systematic Review and Meta-Analysis Protocols (PRIS-MA-P) 64 and was registered with the PROSPERO International Prospective Register of Systematic Reviews, dated 4 January 2021. Based on the actual extractable data types from the included studies, scoping review and/or systematic review will be compared in their V-eligibility. Wherever applicable, the reporting of results will follow PRISMA for Scoping Reviews (PRISMA-ScR), 65 PRISMA 2020 66 and Synthesis Without Meta-analysis (SWiM) guideline. 67 The PRISMA-P checklist for this protocol is available as a separate supplementary document (online supplemental appendix 1). The actual start date of this

Study selection criteria
Human research articles that explicitly claimed to be big data research on environmental health or health services will be included. The selected studies will cover all types of research, including exploratory research, descriptive research, and experimental research. Non-human studies (eg, animal or plants studies) will be excluded. Non-original research articles including reviews articles (eg, literature reviews, systematic reviews, meta-analyses), book reviews, editorials, commentaries, expert opinions, monographs, case reports, case series, protocols, debates, meeting reports, guidelines, subject indexes, round table reports, and forum reports will be excluded. No restrictions will be imposed on the participants, interventions, or comparators. Besides, the eligible article must be written in English and accessible online with full text.

Data sources and search strategy
The search for environmental health research Literature databases, including the WOS, PubMed, Medline (EBSCOhost interface), and ProQuest Central, will be searched, through the application of a search strategy specified in previous reviews that covered the same field of environmental health research. 68 69 Search terms will include "environmental health", "environmental exposure", "environmental illness" and "environmental epidemiology", and the term "big data". No restrictions will be imposed to study type, language, and timespan. The full search strategies for different databases are available (online supplemental appendix 2).
The search for health services research There are two major keywords: (1) "big data" and (2) "health services". All conceptual categories will be formulated from keywords with the Boolean operators supported by the databases. All articles will be searched from same databases of the part of environmental health. Details of the search strategy are provided in online supplemental appendix 3.

Study selection
The studies initially identified through literature databases will be imported into EndNote V.20 citation manager software. 70 EndNote V.20 software will remove duplicates and the no-original research articles including reviews, book reviews, editorials, commentaries, expert opinions, monographs, case reports, case series, protocols, debates, meeting reports, guidelines, subject indexes, round table reports, and forum reports. Two reviewers (TPP, TIL) will independently screen the titles and abstracts of all retrieved studies according to study selection criteria.
The full text of the relevant articles will be downloaded for further evaluation of eligibility. The studies which full-text is not retrievable from databases nor obtainable from the author(s) will be excluded. Studies about data security, equipment or machine health, and product or electronic system health will be excluded. Articles that did not mention the use of big data curation, management, analysis, nor applications will be excluded. The records screened by both reviewers will be compared by cross-tabulation. Any disagreements between two reviewers during study selection will be resolved through discussion with the third reviewer for consensus. The included reports after full-text screening will be assessed for their V-eligibility. Zero V studies and the studies which do not claim to use big data will be excluded. A flow diagram for study search and selection is provided in figure 1.
For the studies that are: (1) not clearly indicated in terms of volume or less than a terabyte in volume; (2) used very simple formats (eg, 2-D tables) of data, or only one data source; (3) not real-time or near real-time in data generation; (4) not trackable or trustworthy in data provenance, questionnaires will be sent to the authors for confirmation. The authors will have one month to reply email and/or return questionnaires.

Information extraction
The studies which meet at least one V (volume, variety, velocity, or veracity) will be included for information extraction and analysis. The text of the following six categories will be extracted from the included studies: 1. Publication information: authors(s) names, article titles, publication years, countries of the first author's research centre or organisation, and journal titles; 2. Types of articles: full research articles, short research reports, and methodology papers; 3. Vs criteria for big data: data characteristics, data collection and processing details (sample sizes, data pro-  Any disagreements in the information extraction process between two reviewers will be resolved through discussion with the third reviewer. Examples of the  Open access information to be analysed by cross-tabulation are as shown in table 2. Moreover, Nvivo, a qualitative data analysis software, will be used to manage and analyse the text data. Relevant and distinctive text excerpts will be coded as themes (nodes) for comparison among studies. Synonyms with varied morphology will be automatically handled in identifying common themes. Then, the software will perform proper text analysis 72 according to the identified themes.

Outcomes
The primary outcomes will be categorised into types of study design, subgroups, and the V-eligibility of the included studies. The secondary outcomes will be the types of big data analytics used in the included studies. A specification of our data analysis plan is given below.

Data synthesis and analysis
Categories regarding the outcomes above will be collected and analysed by basic descriptive statistics with R software. 73 The results will be summarised in table 3.
The text data (ie, characteristics and analysis technologies of big data) will be qualitatively analysed with Nvivo. The eligibility for big data studies will be evaluated by their identities and number of Vs (0-4) in terms of the V criteria.
All the above-mentioned synthesis and analysis processes will be undertaken by two reviewers and any disagreement will be discussed with the third reviewer for consensus. The results will be visualised with tables and graphic charts. The body of evidence will not be assessed

Patient and public involvement
No patient involved.

DISCUSSION
The present study provides the first comprehensive review of big data articles with respect to both environmental health and health services. It used the 4Vsvolume, variety, velocity, and veracity-as criteria to identify whether these studies actually worked with big data and big data analytics techniques. This study seeks to improve the quality of future big data studies in the field of environmental health and health services. The results from the present review will enable researchers to understand how big data studies should be conducted and improve the study quality. This review is the first study to determine which big data technologies have been properly applied to environmental health research.
In reviewing the field of health services, we do not impose restrictions on diseases, conditions, or healthcare domains. This review is the first study to determine how V-eligible big data studies can make a difference to the healthcare service domains.

Open access
This study has several limitations. Firstly, research papers could be too obscure in reporting their V-eligibility. Email queries with online questionnaires will be sent to the authors for confirmation of information. Secondly, the present study mainly involves descriptive statistics of the extracted information to outline how big data are used in environmental health and health services research. Advanced statistics and further hypothesis-based studies will be designed after the present study. Lastly, this study does not reflect a representational picture of how big data are used in the broad field of medicine, but only that in environmental health and health services research.

ETHICS AND DISSEMINATION Ethics approval
All data reviewed by the present study have been published and are publicly available; thus, ethics approval is not required for this study.

Publication plan
This protocol has been registered with the PROSPERO. The conduct and reporting of the review will follow PRISMA-ScR, PRISMA 2020, and SWiM. The results of this study will be disseminated through a peer-reviewed journal.