A Review of Data Quality Assessment Methods for Public Health Information Systems

High quality data and effective data quality assessment are required for accurately evaluating the impact of public health interventions and measuring public health outcomes. Data, data use, and data collection process, as the three dimensions of data quality, all need to be assessed for overall data quality assessment. We reviewed current data quality assessment methods. The relevant study was identified in major databases and well-known institutional websites. We found the dimension of data was most frequently assessed. Completeness, accuracy, and timeliness were the three most-used attributes among a total of 49 attributes of data quality. The major quantitative assessment methods were descriptive surveys and data audits, whereas the common qualitative assessment methods were interview and documentation review. The limitations of the reviewed studies included inattentiveness to data use and data collection process, inconsistency in the definition of attributes of data quality, failure to address data users’ concerns and a lack of systematic procedures in data quality assessment. This review study is limited by the coverage of the databases and the breadth of public health information systems. Further research could develop consistent data quality definitions and attributes. More research efforts should be given to assess the quality of data use and the quality of data collection process.

(PHIS) must first undergo collection, storage, processing, and compilation. The procured data can then be retrieved, analyzed, and disseminated. Finally, the data will be used for decision-making to guide public health practice [5]. Therefore, the data flows in a public health practice lifecycle consist of three phases: data, data collection process and use of data.
PHIS, whether paper-based or electronic, are the repositories of public health data. The systematic application of information and communication technologies (ICTs) to public health has seen the proliferation of computerized PHIS around the world [14][15][16]. These distributed systems collect coordinated, timely, and useful multi-source data, such as those collected by nation-wide PHIS from health and other sectors [17]. These systems are usually population-based, and recognized by government-owned public health agencies [18].
The computerized PHIS are developed with broad objectives, such as to provide alerts and early warning, support public health management, stimulate research, and to assist health status and trend analyses [19]. Significant advantages of PHIS are their capability of electronic data collection, as well as the transmission and interchange of data, to promote public health agencies' timely access to information [15,20]. The automated mechanisms of numeric checks and alerts can improve validity and reliability of the data collected. These functions contribute to data management, thereby leading to the improvement in data quality [21,22].
Negative effects of poor data quality, however, have often been reported. For example, Australian researchers reported coding errors due to poor quality documentations in the clinical information systems. These errors had consequently led to inaccurate hospital performance measurement, inappropriate allocation of health funding, and failure in public health surveillance [23].
The establishment of information systems driven by the needs of single-disease programs may cause excessive data demand and fragmented PHIS systems, which undermine data quality [5,24]. Studies in China, the United Kingdom and Pakistan reported data users' lack of trust in the quality of AIDS, cancer, and health management information systems due to unreliable or uncertain data [25][26][27].
Sound and reliable data quality assessment is thus vital to obtain the high data quality which enhances users' confidence in public health authorities and their performance [19,24]. As countries monitor and evaluate the performance and progress of established public health indicators, the need for data quality assessment in PHIS that store the performance-and-progress-related data has never been greater [24,28,29]. Nowadays, data quality assessment that has been recommended for ensuring the quality of data in PHIS becomes widespread acceptance in routine public health practice [19,24].
Data quality in public health has different definitions from different perspectives. These include: "fit for use in the context of data users" [30], (p. 2); "timely and reliable data essential for public health core functions at all levels of government" [31], (p. 114) and "accurate, reliable, valid, and trusted data in integrated public health informatics networks" [32]. Whether the specific data quality requirements are met is usually measured along a certain number of data quality dimensions. A dimension of data quality represents or reflects an aspect or construct of data quality [33].
Data quality is recognized as a multi-dimensional concept across public health and other sectors [30,[33][34][35]. Following the "information chain" perspective, Karr et al. used "three hyper-dimensions" (i.e., process, data and user) to group a set of conceptual dimensions of data quality [35]. Accordingly, the methods for assessment of data quality must be useful to assess these three dimensions [35]. We adopted the approach of Karr et al. because their typology provided a comprehensive perspective for classifying data quality assessment. However, we replace "process" by "data collection process" and "user" by "data use". "Process" is a broad term and may be considered as the whole process of data flows, including data and use of data. "User" is a specific term related to data users or consumers and may ignore the use of data. To accurately reflect the data flows in the context of public health, we define the three dimensions of data quality as data, data use and data collection process. The dimension of data focuses on data values or data schemas at record/table level or database level [35]. The dimension of data use, related to use and user, is the degree and manner in which data are used [35]. The dimension of data collection process refers to the generation, assembly, description and maintenance of data [35] before data are stored in PHIS.
Data quality assessment methods generally base on the measurement theory [35][36][37][38]. Each dimension of data quality consists of a set of attributes. Each attribute characterizes a specific data quality requirement, thereby offering the standard for data quality assessment [35]. Each attribute can be measured by different methods; therefore, there is flexibility in methods used to measure data quality [36][37][38]. As the three dimensions of data quality are embedded in the lifecycle of public health practice, we propose a conceptual framework for data quality assessment in PHIS ( Figure 1).

Figure 1.
Conceptual framework of data quality assessment in public health practice.
Although data quality has always been an important topic in public health, we have identified a lack of systematic review of data quality assessment methods for PHIS. This is the motivation for this study because knowledge about current developments in methods for data quality assessment is essential for research and practice in public health informatics. This study aims to investigate and compare the methods for data quality assessment of PHIS so as to identify possible patterns and trends emerging over the first decade of the 21st century. We take a qualitative systematic review approach using our proposed conceptual framework.

Literature Search
We identified publications by searching several electronic bibliographic databases. These included Scopus, IEEE Xplore, Web of Science, ScienceDirect, PubMed, Cochrane Library and ProQuest. Because many public health institutes also published guidelines, frameworks, or instruments to guide the institutional approach to assess data quality, some well-known institutions' websites were also reviewed to search for relevant literature. The following words and MeSH headings were used individually or in combination: "data quality", "information quality", "public health", "population health", "information system *", "assess *", "evaluat *". ("*" was used to find the variations of some word stems.) The articles were confined to those published in English and Chinese language.
The first author performed the literature search between June 2012 and October 2013. The inclusion criteria were peer-refereed empirical studies or institutional reports of data quality assessment in public health or PHIS during the period 2001-2013. The exclusion criteria were narrative reviews, expert opinion, correspondence and commentaries in the topic area. To improve coverage, a manual search of the literature was conducted to identify papers referenced by other publications, papers and well-known authors, and papers from personal databases.

Selection of Publications
Citations identified in the literature search were screened by title and abstract for decisions about inclusion or exclusion in this review. If there was uncertainty about the relevance of a citation, the full-text was retrieved and checked. A total of 202 publications were identified and were manually screened. If there was uncertainty about whether to include a publication, its relevance was checked by the fourth author. Finally 39 publications that met the inclusion criteria were selected. The screening process is summarized in Figure 2.

Data Abstraction
The selected publications were stored in an EndNote library. Data extracted from the publications included author, year of publication, aim of data quality assessment, country and context of the study, function and scope of the PHIS, definition of data quality, methods for data quality assessment, study design, data collection methods, data collected, research procedure, methods for data analysis, key findings, conclusions and limitations.
The 39 publications were placed in two groups according to whether they were published by a public health institution at national or international level or by individual researchers. If the article was published by the former, it is referred to as an institutional publication, if by the latter, as a research paper.

Results
Of the 39 publications reviewed, 32 were peer-refereed research papers and seven were published by public health institutions. The institutional publications are listed in Table 1. 27 of the 39 reviewed publications were published between 2008 and 2013. There was a trend of increasing numbers of research papers per year, suggesting an increasing research focus on data quality with the wider adoption of computerised PHIS in recent years.
The results are organized as follows. First, the aims of the studies are given. This is followed by context and scope identified in Section 3.2. Section 3.3 examines the methods for data quality assessment. A detailed summary of the findings concludes the results in Section 3.4. For each section, a comparison between institutional publications and research papers was conducted, where this was possible and meaningful.

Context and Scope of the Studies
The contexts of the studies were primarily confined to the public health domain, with other settings addressed occasionally.
Two types of public health context were covered in the institutional publications. The first included specific disease and health events, such as AIDS, tuberculosis, malaria, and immunization [15,34,42]. The latter was the public health system. This included public health project/program data management and reporting, routine health information systems, and PHIS under a national health institute [34,40,41,44,45].
The public health data from information systems operated by agencies other than public health were also assessed. They include the National Coronial Information System managed by the Victorian Department of Justice in Australia, women veteran mortality information maintained by the U.S. Department of Veterans' Affairs, and military disability data from U.S. Navy Physical Evaluation Board [47,52,64].

Methods for Data Quality Assessment
Analysis of methods for data quality assessment in the reviewed publications is presented in three sections, based on the dimensions of data quality that were covered: data, data use or data collection process. Seven perspectives were reviewed, including quality attributes for each dimension, major measurement indicators for each attribute, study design/method of assessment, data collection methods, data analysis methods, contributions and limitations.

Methods for Assessment of the Dimension of Data
In this section, the concept of data quality is a narrow one, meaning the quality of the dimension of data. All of the institutional publications and 28 research papers, a total of 35 articles, conducted assessment of the quality of data [15,22,30,34,40,42,[72][73][74]. Matheson et al. introduced the attributes of data quality but did not give assessment methods [71]. Additional information is provided in Table A1.

Quality Attributes of Data and Corresponding Measures
A total of 49 attributes were used in the studies to describe data quality, indicating its multi-dimensional nature. Completeness, accuracy and timeliness were the three attributes measured most often.
The attributes of data quality are grouped into two types: those of good data quality and those of poor data quality (see Table 2). Table 2. Attributes of data quality.

Item Attribute
High data quality (38) Completeness, accuracy or positional accuracy, timeliness or up-datedness or currency, validity, periodicity, relevance, reliability, precision, integrity, confidentiality or data security, comparability, consistency or internal consistency or external consistency, concordance, granularity, repeatability, readily useableness or usability or utility, objectivity, ease with understanding, importance, reflecting actual sample, meeting data standards, use of standards, accessibility, transparency, representativeness, disaggregation, data collection method or adjustment methods or data management process or data management Poor data quality (11) Missing data, under-reporting, inconsistencies, data errors or calculation errors or errors in report forms or errors resulted from data entry, invalid data, illegible hand writing, non-standardization of vocabulary, and inappropriate fields Inconsistencies in the definition of attributes were identified. The same attribute was sometimes given different meanings by different researchers. One example of this was "completeness". Some institutions required conformity to the standard process of data entry, such as filling in data elements in the reporting forms [15,40,41,44]. Completeness was represented as the percentage of blank or unknown data, not zero/missing, or proportion of filling in all data elements in the facility report form [15,40,41,44]. The ME PRISM, instead, defined completeness as the proportion of facilities reporting in an administrative area [40]. The other definition of completeness was the correctness of data collection methods in ME DQA, i.e., "complete list of eligible persons or units and not just a fraction of the list" [34].
Of the 19 research papers including completeness as an attribute, 12 measured the completeness of data elements as "no missing data or blank" [22,46,[48][49][50][51]57,63,69,[72][73][74]. Dixon et al. defined completeness as considering both filling in data elements and data collection methods [54]. Four studies measured completeness of data by the sample size and the percentage of health facilities that completed data reports [61,65,66,68]. The remaining two studies did not give precise definitions [51,64].
On the other hand, different attributes could be given the same meaning. For example, the ME DQA defined accuracy as "validity", which is one of two attributes of data quality in CDC's Guidelines [15,34]. Makombe et al. considered that data were accurate if none of the examined variables in the site report was missing [49]. This is similar to the definition of completeness, as "no missing data" or "no blank of data elements" in the reports by other studies.

Study Design
Quantitative methods were used in all studies except that of Lowrance et al. who used only qualitative methods [63]. Retrospective, cross-sectional survey was commonly used for quantitative studies. Pereira et al. conducted a multi-center randomized trial [72].
Qualitative methods, including review of publications and documentations, interviews with key informants, and field observations, were also used in 8 studies [34,45,50,57,61,65,69,72]. The purpose of the application of qualitative methods was primarily to provide the context of the findings from the quantitative data. For example, Hahn et al. conducted a multiple-case study in Kenya to describe clinical information systems and assess the quality of data. They audited a set of selected data tracer items, such as blood group and weight, to assess data completeness and accuracy. Meanwhile, they obtained end-users' views of data quality from structured interviews with 44 staff members and qualitative in-depth interviews with 15 key informants [50].
The data collection period ranged from one month to 16 years [67,74]. The study with the shortest time frame of one month had the maximum number of data records, 7.5 million [67], whereas the longest study, from 1970 to 1986, collected only 404 cases of disease [74]. The sample size of users ranged from 10 to 100 [45,61].
In the publications with data as the study subject, a certain number of data variables were selected, but the reason(s) for the section was (were) not always given. They included elements of demographics such as age, gender, and birth date, and specific information such as laboratory testing results, and disease code. The minimum and maximum number of data variables was 1 and 30, respectively [58,59].
The qualitative data were transcribed first before semantic analysis by theme grouping methods [63].

Methods for Assessment of the Dimension of Data Use
Ten studies, including one institutional publication and nine research papers, are reviewed in this section [26,27,40,45,50,52,61,62,70,71]. Five studies were concerned with the assessment of data use and the factors influencing data use [26,27,52,70,71]. The other five included assessment of data use, but this was not always highlighted [40,45,50,61,62]. Details are given in Table A2.

Quality Attributes of Data Use and Corresponding Measures
A total of 11 attributes were used to define the concept of data use. These were: trend in use, use of data or use of information, system use or usefulness of the system, intention to use, user satisfaction, information dissemination or dissemination of data, extent of data source recognition and use or specific uses of data, and existence and contents of formal information strategies and routines.
The measures fall into three categories: data use for the purpose of action, planning and research; strategies and mechanisms of data use; and awareness of data sources and data use.
The first category of measures was mentioned in eight studies [26,40,45,50,52,61,70,71]. For example, actioned requests from researchers, the number of summaries/reports produced, and the percentage of report use [40,52,71]. Freestone et al. calculated actioned requests from researchers who do not have access to the PHIS [52]. The measurement indicators in ME PRISM were report production and display of information. They were assessed by whether and how many reports containing data from the PHIS were compiled, issued, fed back and displayed for a set time frame [40]. Saeed et al. assessed the use of data by predefined criteria, including the availability of comprehensive information, whether data were used for planning and action at each level, and whether feedback was given to the lower organizational level of the public health system [61].
The second category of measures was assessed in five studies [26,27,45,61,70]. The criteria of the measurement included the availability of a feedback mechanism, policy and advocacy, the existence and the focus of formal information strategies, and routines of data use [26,45,70].
The third category measured users' awareness of data use which was reported in two studies [26,62]. Petter and Fruhling applied the DeLone and McLean information systems success model [62]. They used the framework to evaluate system use, intention to use, and user satisfaction in 15 questions by considering the context of the PHIS, which was an emergency response medical information system. Wilkinson and McCarthy recommended examining whether the studied information systems were recognized by the users in order to assess the extent of data source recognition among respondents [26].

Study Design
Three studies only used quantitative methods [40,52,62] and three studies only used qualitative methods [27,50,70]. The remaining four studies combined qualitative and quantitative methods [26,45,61,71]. Interviews, questionnaire surveys, reviews of documentation and abstracts of relevant data were used in the studies.

Data Collection Methods
The sources of information for the study subjects included users and stakeholders, existing documents, and data from the PHIS. Study subjects were all users in six studies [26,27,45,50,62,70], and all data in the study by Freestone et al. [52]. Both user and documentation were study subjects in two studies [40,61], and together with data in another study [71]. Convenience or purposive sampling was generally used.
Among nine studies whose study subjects were users, structured and semi-structured questionnaire surveys, group discussions, and in-depth interviews were used to collect data. Use of self-assessment, face-to-face communication, telephone, internet telephony, online, email, facsimile and mail were reported in the studies. For example, Wilkinson and McCarthy used a standardized semi-structured questionnaire for telephone interviews with key informants [26]. Petter and Fruhling used an online survey as well as facsimile and mail to the PHIS users [62]. Qazi and Al administered in-depth, face-to-face and semi-structured interviews with an interview guide [27]. Saeed et al. predefined each criterion for data use and measured it by a 3-point Likert scale. They assessed each criterion through interviewing key informants and consulting stakeholders. Desk review of important documents, such as national strategic plans, guidelines, manuals, annual reports and databases was also reported in their study [61].
Four studies assessing data use by data and documentation either queried information directly from the data in the studied PHIS, if applicable, or collected evidence from related documents such as reports, summaries, and guidelines [40,52,61,71]. The data to be collected included actioned requests, the number of data linked to action, and the number of data used for planning. Time for data collection varied without explanation, such as 12 months in ME PRISM or six years by Freestone et al. [40,52].

Data Analysis Methods
The data collected from qualitative studies were usually processed manually, organized thematically or chronologically. They were either analyzed by classification of answers, grouping by facility or respondent's role, or categorization of verbatim notes into themes.
Various strategies were applied for quantitative data. For example, Wilkinson and McCarthy counted the same or similar responses to indicate frequency of beliefs/examples across participants [26]. Data in their study were analyzed individually, by role and aggregated level. Some correlational analyses, such as Pearson's r for parametric data and Spearman's Rho for non-parametric data, were conducted to identify possible relationships between data use, perceptions of data, and organizational factors. Petter and Fruhling conducted hypothesis analysis in structured questionnaire with a 7-point Likert scale for all quantitative questions [62]. Due to the small sample size of 64 usable responses, they used summative scales for each of the constructs. All of the items used for a specific construct were averaged to obtain a single value for this construct. Then, using this average score, each hypothesis was tested using simple regression.

Methods for Assessment of the Dimension of Data Collection Process
Although the aim of assessing data flow or the process of data collection was only stated in two studies, another 14 articles were found that implicitly assessed data collection process [22,30,34,40,42,45,50,52,55,[58][59][60]65,67,69,70]. These articles were identified through a detailed content analysis. For example, data collection process assessment activities were sometimes initiated by identification of the causes of poor data quality [52,55,59]. Or data collection process was considered as a component of the evaluation of the effectiveness of the system [22,34,42,45,58,60,65,69]. Three studies led by two institutions, CIHI and MEASURE Evaluation Project, assessed data collection process while conducting assessment of the quality of the data, [30,40,50]. Details are given in Table A3.

Quality Attributes of Data Collection Process and Corresponding Measures
A total of 23 attributes of data collection process were identified. These were: quality index or quality scores or functional areas, root causes for poor data quality, metadata or metadata documentation or data management or case detection, data flow or information flow chart or data transmission, data collection or routine data collection or data recording or data collection and recording processes or data collection procedures, data quality management or data quality control, statistical analysis or data compilation or data dissemination, feedback, and training.
Only four studies explicitly defined the attributes of the dimension of data collection process, two of them from institutions [40,45,52,70]. Data collection was the most-used attribute in six publications [34,40,52,65,67,69,70]. The next most-assessed attribute is data management processes or data control reported in four publications [34,45,67,69].
Data collection process was sometimes considered a composite concept in six studies, four of them proposed by institutions [30,34,42,45,58,60]. For example, the quality index/score was composed of five attributes: recording practices, storing/reporting practices, monitoring and evaluation, denominators, and system design (the receipt, processing, storage and tabulation of the reported data) [42,58,60]. Metadata documentation or metadata dictionary cover dataset description, methodology, and data collection, capture, processing, compilation, documentation, storage, analysis and dissemination [30,45]. The ME DQA assessed five functional areas, including structures, functions and capabilities, indicator definitions and reporting guidelines, data collection and reporting forms and tools, data management processes, and links with the national reporting system [34].

Data Collection and Analysis Methods
The study subjects included managers or users of the PHIS, the documentation of instructions and guidelines of data management for the PHIS, and some procedures of data collection process. The study subjects were entirely users in eight studies [22,30,40,45,58,59,67,70]. Corriols et al. and Dai et al. only studied documentation such as evaluation reports on the PHIS including deficiency in the information flow chart and non-reporting by physicians [55,69]. Data collection process was studied in six publications [34,45,50,52,60,65]. Of these, four studies combined data collection procedures with users and documentation [34,42,52,65], while Hahn et al. only observed data collection procedures and Ronveaux et al. surveyed users and observed data collection procedures for a hypothetical population [50,60].
The data collection methods included field observation, questionnaire surveys, consensus development, and desk review of documentation. Field observations were conducted either in line with a checklist or in an informal way [34,40,50,52,60,65]. Lin et al. made field observations of the laboratory staff dealing with specimens and testing at the early stage of the data collection process [65]. Freestone et al. observed data coders' activities during the process of data geocoding and entry [52]. Hahn et al. followed the work-through in study sites [50]. WHO DQA conducted field observations on sites of data collection, processing and entry [42], while Ronveaux et al. observed workers at the health-unit level who completed some data collection activities for 20 hypothetical children [60]. ME DQA made follow-up on-site assessment of off-site desk-reviewed documentation at each level of the PHIS [34].
Consensus development was mainly used in group discussion and meetings, guided by either structured questionnaires or data quality issues [45,59]. Ancker et al. held a series of weekly team meetings over about four months with key informants involved in data collection [59]. They explored the root causes of poor data quality in line with the issues identified from assessment results. WHO HMN organized group discussions with approximately 100 major stakeholders [45]. Five measures related to data collection process were contained in a 197-item questionnaire. The consensus to each measure was reached through self-assessment, individual or group scoring to yield a percentage rating [45].
Desk review of documentation was reported in six studies [34,52,55,65,69,70]. The documentation included guidelines, protocols, official evaluation reports and those provided by data management units. The procedures for appraisal and adoption of relevant information were not introduced in the studies.
Data analysis methods for quantitative studies were mainly descriptive statistics. Most papers did not present the methods for analysis of the qualitative data. Information retrieved from the qualitative study was usually triangulated with findings from quantitative data.

Summary of the Findings
Four major themes of the results have emerged after our detailed analysis, which are summarized in this section.
The first theme is there are differences between the seven institutional and the 32 individual research publications in their approach to data quality assessment, in terms of aims, context and scope. First, the effectiveness of the PHIS was more of an institutional rather than a researcher's interest. It was covered in all of the institutional publications but only in one-third of the research papers. Second, the disease-specific public health contexts covered by United Nations' MDGs, maternal health, children's health, and HIV/AIDS, were the area most often studied by researchers. Whereas the institutions also paid attention to the routine PHIS. Third, the institutions tended to evaluate all levels of data management whereas most research studies were focused on a single level of analysis, either record collection or management.
The second theme is coverage of the three dimensions of data quality was not equal. The dimension of data was most frequently assessed (reported in 35 articles). Data use was explicitly assessed in five studies and data collection process in one. Implicit assessment of data use and data collection process was found in another five and 15 papers, respectively. The rationale for initiating these implicit assessments was usually to identify factors arising from either data use or data collection process while assessing the quality of data. Within studies that considered more than one dimension of data quality, 15 assessed both data and data collection process, seven assessed data and data use and one, both data use and data collection process. Only four studies assessed all three dimensions of data quality.
The third emerging theme is a lack of clear definition of the attributes and measurement indicators of each dimension of data quality. First, a wide variation of the definition of the key terms was identified, including the different terms for the same attribute, and the same term to refer to distinct attributes. The definition of attributes and their associated measures was sometimes given based on intuition, prior experience, or the underlying objectives unique to the PHIS in a specific context.
Second, the attributes of the quality of data were relatively developed than those for the dimensions of data use and data collection process. Most definitions of data quality attributes and measures are referred to the dimension of data as opposed to the other two dimensions, the attributes of which were primarily vague or obscure. One clear gap is the absence of the attributes of the dimension of data collection process.
Third, a consensus has not been reached as to what attributes should be measured. For example, a large variety existed in the number of attributes measured in the studies varied between 1 and 8, in a total of 49 attributes. The attribute of data quality in public health is often measured positively in terms of what it is. The three most-used attributes of good data quality were completeness, accuracy, and timeliness. The institutions tended to assess more attributes of data quality than individual researchers. The number of attributes reported in research papers was no more than four, while the institutions assessed at least four attributes.
The last emerging theme of the results is methods of assessment lack systematic procedures. Quantitative data quality assessment primarily used descriptive surveys and data audits, while qualitative data quality assessment methods include primarily interview, documentation review and field observation. Both objective and subjective strategies were identified among the methods for assessing data quality. The objective approach applies quantifiable measurements to directly examine the data according to a set of data items/variables/elements/tracer items. The subjective approach measures the perceptions of the users and stakeholders of the PHIS. However, only a small minority of the reviewed studies used both types of assessment. Meanwhile, field verification of the quality of data is not yet a routine practice in data quality assessment. Only five studies conducted field observations for data or for data collection process and they were usually informal. The reliability and validity of the study was rarely reported.

Discussion
Data are essential to public health. They represent and reflect public health practice. The broad application of data in PHIS for the evaluation of public health accountability and performance has raised the awareness of public health agencies of data quality, and of methods and approaches for its assessment. We systematically reviewed the current status of quality assessment for each of the three dimensions of data quality: data, data collection process and data use. The results suggest that the theory of measurement has been applied either explicitly or implicitly in the development of data quality assessment methods for PHIS. The majority of previous studies assessed data quality by a set of attributes using certain measures. Our findings, based on the proposed conceptual framework of data quality assessment for public health, also identified the gaps existed in the methods included in this review.
The importance of systematic, scientific data quality assessment needs to be highlighted. All three dimensions of data quality, data, data use and data collection process, need to be systematically evaluated. To date, the three dimensions of data quality were not given the same weight across the reviewed studies. The quality of data use and data collection process has not received adequate attention. This lack of recognition of data use and data collection process might reflect a lack of consensus on the dimensions of data quality. Because of the equal contributions of these three dimensions to data quality, they should be given equal weight in data quality assessment. Further development in methods to assess data collection process and data use is required.
Effort should also be directed towards clear conceptualisation of the definitions of the relevant terms that are commonly used to describe and measure data quality, such as the dimensions and attributes of data quality. The lack of clear definition of the key terms creates confusions and uncertainties and undermines the validity and reliability of data quality assessment methods. An ontology-based exploration and evaluation from the perspective of data users will be useful for future development in this field [33,75]. Two steps that involve conceptualization of data quality attributes and operationalization of corresponding measures need to be taken seriously into consideration and rationally followed as shown in our proposed conceptual framework.
Data quality assessment should use mixed methods (e.g., qualitative and quantitative assessment methods) to assess data from multiple sources (e.g., records, organisational documentation, data collection process and data users) and used at different levels of the organisation [33,35,36,38,75,76]. More precisely, we strongly suggest that subjective assessments of end-users' or customers' perspectives be an indispensible component in data quality assessment for PHIS. The importance of this strategy has long been articulated by the researchers [33,75,76]. Objective assessment methods assess the data that were already collected and stored in the PHIS. Many methods have been developed, widely accepted and used in practice [38,76]. On the other hand, subjective assessments provide a supplement to objective data quality assessment. For example, interview is useful for the identification of the root causes of poor data quality and for the design of effective strategies to improve data quality. Meanwhile, field observation and validation is necessary wherever it is possible because reference of data to the real world will give data users confidence in the data quality and in application of data to public health decision-making, action, and outcomes [52]. The validity of a study would be doubtful if the quality of data could not be verified in the field [36], especially when the data are come from a PHIS consisting of secondary data.
To increase the rigor of data quality assessment, the relevant statistical principles for sample size calculation, research design, measurement and analysis need to be adhered to. Use of convenience or specifically chosen sampling methods in 24 studies included in this review reduced the representativeness and generalizability of the findings of these studies. At the same time, reporting of data quality assessment needs to present the detailed procedures and methods used for the study, the findings and limitations. The relatively simple data analysis methods using only descriptive statistics could lead to loss of useful supportive information.
Finally, to address the gaps identified in this review, we suggest re-prioritizing the orientation of data quality assessment in future studies. Data quality is influenced by technical, organizational, behavioural and environmental factors [35,41]. It covers large information systems contexts, specific knowledge and multi-disciplinary techniques [33,35,75]. Data quality in the reviewed studies is frequently assessed as a component of the quality or effectiveness or performance of the PHIS. This may reflect that the major concern of public health is in managerial efficiency, especially of the PHIS institutions. Also, this may reflect differences in the resources available to, and the responsibilities of institutions and individual researchers. However, data quality assessment hidden within other scopes may lead to ignorance of data management and thereby the unawareness of data quality problems enduring in public health practice. Data quality needs to be positioned at the forefront of public health as a distinct area that deserves specific scientific research and management investment.
While this review provides a detailed overview of data quality assessment issues, there are some limitations in its coverage, constrained by the access to the databases and the breadth of public health information systems making it challenge to conduct systematic comparison among studies. The search was limited by a lack of subject headings for data quality of PHIS in MeSH terms. This could cause our search to miss some relevant publications. To compensate for this limitation, we used the strategy of searching well-known institutional publications and manually searching the references of each article retrieved.
Our classification process was primarily subjective. It is possible that some original researchers disagree with our interpretations. Each assessment method has contributions and limitations which make the choices difficult. We provided some examples of approaches to these issues.
In addition, our evaluation is limited by an incomplete presentation of details in some of the papers that we reviewed. A comprehensive data quality assessment method includes a set of guidelines and techniques that defines a rational process to assess data quality [37]. The detailed procedure of data analysis, data quality requirements analysis, and identification of critical attributes is rarely given in the reviewed papers. A lack of adequate detail in the original studies could have affected the validity of some of our conclusions.

Conclusions
Public health is a data-intensive field which needs high-quality data to support public health assessment, decision-making and to assure the health of communities. Data quality assessment is important for public health. In this review of the literature we have examined the data quality assessment methods based on our proposed conceptual framework. This framework incorporates the three dimensions of data quality in the assessment methods for overall data quality: data, data use and data collection process. We found that the dimension of the data themselves was most frequently assessed in previous studies. Most methods for data quality assessment evaluated a set of attributes using relevant measures. Completeness, accuracy, and timeliness were the three most-assessed attributes. Quantitative data quality assessment primarily used descriptive surveys and data audits, while qualitative data quality assessment methods include primarily interview, documentation review and field observation.
We found that data-use and data-process have not been given adequate attention, although they were equally important factors which determine the quality of data. Other limitations of the previous studies were inconsistency in the definition of the attributes of data quality, failure to address data users' concerns and a lack of triangulation of mixed methods for data quality assessment. The reliability and validity of the data quality assessment were rarely reported. These gaps suggest that in the future, data quality assessment for public health needs to consider equally the three dimensions of data quality, data, data use and data process. More work is needed to develop clear and consistent definitions of data quality and systematic methods and approaches for data quality assessment.
The results of this review highlight the need for the development of data quality assessment methods. As suggested by our proposed conceptual framework, future data quality assessment needs to equally pay attention to the three dimensions of data quality. Measuring the perceptions of end users or consumers towards data quality will enrich our understanding of data quality issues. Clear conceptualization, scientific and systematic operationalization of assessment will ensure the reliability and validity of the measurement of data quality. New theories on data quality assessment for PHIS may also be developed.           Table A2. Characteristics of the methods for assessment of data use reported in the 10 publications included in the review.

Authors Year Attributes Major measures Study design Data collection methods Data analysis methods Contribution Limitations
Freestone et al.
2012 [52] Trends in use Actioned requests from researchers in a set period of time