Toward a comprehensive evidence map of overview of systematic review methods: paper 2—risk of bias assessment; synthesis, presentation and summary of the findings; and assessment of the certainty of the evidence
Systematic Reviews volume 7, Article number: 159 (2018)
Overviews of systematic reviews (SRs) attempt to systematically retrieve and summarise the results of multiple systematic reviews. This is the second of two papers from a study aiming to develop a comprehensive evidence map of the methods used in overviews. Our objectives were to (a) develop a framework of methods for conducting, interpreting and reporting overviews (stage I)—the Methods for Overviews of Reviews (MOoR) framework—and (b) to create an evidence map by mapping studies that have evaluated overview methods to the framework (stage II). In the first paper, we reported findings for the four initial steps of an overview (specification of purpose, objectives and scope; eligibility criteria; search methods; data extraction). In this paper, we report the remaining steps: assessing risk of bias; synthesis, presentation and summary of the findings; and assessing certainty of the evidence arising from the overview.
In stage I, we identified cross-sectional studies, guidance documents and commentaries that described methods proposed for, or used in, overviews. Based on these studies, we developed a framework of possible methods for overviews, categorised by the steps in conducting an overview. Multiple iterations of the framework were discussed and refined by all authors. In stage II, we identified studies evaluating methods and mapped these evaluations to the framework.
Forty-two stage I studies described methods relevant to one or more of the latter steps of an overview. Six studies evaluating methods were included in stage II. These mapped to steps involving (i) the assessment of risk of bias (RoB) in SRs (two SRs and three primary studies, all reporting evaluation of RoB tools) and (ii) the synthesis, presentation and summary of the findings (one primary study evaluating methods for measuring overlap).
Many methods have been described for use in the latter steps in conducting an overview; however, evaluation and guidance for applying these methods is sparse. The exception is RoB assessment, for which a multitude of tools exist—several with sufficient evaluation and guidance to recommend their use. Evaluation of other methods is required to provide a comprehensive evidence map.
Overviews of systematic reviews aim to systematically retrieve, critically appraise and synthesise the results of multiple systematic reviews (SRs) . Overviews of reviews (also called umbrella reviews, meta-reviews, reviews of reviews; but referred to in this paper as ‘overviews’ ) have grown in number in recent years, largely in response to the increasing number of SRs . Overviews have many purposes including mapping the available evidence and identifying gaps in the literature, summarising the effects of the same intervention for different conditions or populations or examining reasons for discordance of findings and conclusions across SRs [4,5,6]. A noted potential benefit of overviews is that they can address a broader research question than the constituent SRs, since overviews are able to capitalise on previous SR efforts .
The steps and many of the methods used in the conduct of SRs are directly transferrable to overviews. However, overviews involve unique methodological challenges that primarily stem from a lack of alignment between the PICO (Population, Intervention, Comparison, Outcome) elements of the overview question and those of the included SRs, and overlap, where the same primary studies contribute data to multiple SRs . For example, overlap can lead to challenging scenarios such as how to deal with discordant risk of bias assessments of the same primary studies across SRs (often further complicated by the use of different risk of bias/quality tools) or how to synthesize results from multiple meta-analyses where the same studies contribute to more than one pooled analysis. Authors need to plan for these scenarios, which may require the application of different or additional methods to those used in systematic reviews of primary studies.
Two recent reviews of methods guidance for conducing overviews found that there were important gaps in the guidance on the conduct of overviews [8, 9]. The results of our first paper—which identified methods for the initial steps in conducting an overview and collated the evidence on the performance of these methods —aligned with these findings. We further identified that there was a lack of studies evaluating the performance of overview methods and limited empirical evidence to inform methods decision-making in overviews .
This paper is the second of two papers, which together, aim to provide a comprehensive framework of overview methods and the evidence underpinning these methods—an evidence map of overview methods. In doing so, we aim to help overview authors plan for common scenarios encountered when conducting an overview and enable prioritisation of methods development and evaluation.
The objectives of this study were to (a) develop a comprehensive framework of methods that have been used, or may be used, in conducting, interpreting and reporting overviews of systematic reviews of interventions (stage I)—the Methods for Overviews of Reviews (MOoR) framework; (b) map studies that have evaluated these methods to the framework (creating an evidence map of overview methods) (stage II); and (c) identify unique methodological challenges of overviews and methods proposed to address these.
In the first paper, we presented the methods framework, along with the studies that had evaluated those methods mapped to the framework (the evidence map) for the four initial steps of conducting an overview: (a) specification of the purpose, objectives and scope of the overview; (b) specification of the eligibility criteria; (c) search methods and (d) data extraction methods . In this second companion paper, we present the methods framework and evidence map for the subsequent steps in conducting an overview: (e) assessment of risk of bias in SRs and primary studies; (f) synthesis, presentation and summary of the findings and (g) assessment of the certainty of evidence arising from the overview (Fig. 1).
We use the term ‘methods framework’ (or equivalently, ‘framework of methods’) to describe the organising structure we have developed to group-related methods, and against which methods evaluations can be mapped. The highest level of this structure is the broad steps of conducting an overview (e.g. synthesis, presentation and summary of the findings). The methods framework, together with the studies that have evaluated these methods, form the evidence map of overview methods.
A protocol for this study has been published , and the methods have been described in detail in the first paper in the series . The methods for the two research stages (Fig. 2) are now briefly described, along with deviations from the planned methods pertaining to this second paper. A notable deviation from our protocol is that we had planned to include the step ‘interpretation of findings and drawing conclusions’, but after reviewing the literature, felt that there was overlap between this step and the ‘assessment of certainty of the evidence arising from the overview’ step, and so consolidated the identified methods into the latter step.
Stage I: development and population of the framework of methods
Our main search strategy included searching MEDLINE from 2000 onwards and the following methods collections: Cochrane Methodology Register, Meth4ReSyn library, Scientific Resource Center Methods library of the AHRQ Effective Health Care Program and Cochrane Colloquium abstracts. Searches were run on December 2, 2015 (see Additional file 1 for search strategies). These searches were supplemented by methods articles we had identified through a related research project, examination of reference lists of included studies, contact with authors of conference posters, and citation searches (see Paper 1  for details).
We identified articles describing methods used, or recommended for use, in overviews of systematic reviews of interventions.
Articles describing methods for overviews of systematic reviews of interventions
Articles examining methods used in a cross-section or cohort of overviews
Guidance (e.g. handbooks and guidelines) for undertaking overviews
Commentaries or editorials that discuss methods for overviews
Articles published in languages other than English
Articles describing methods for network meta-analysis
Articles exclusively about methods for overviews of other review types (i.e. not of interventions)
We populated the framework with methods that are different or additional to those required to conduct a SR of primary research. Methods evaluated in the context of other ‘overview’ products, such as guidelines, which are of relevance to overviews, were included.
The eligibility criteria were piloted by three reviewers independently on a sample of articles retrieved from the search to ensure consistent application.
Two reviewers independently reviewed the title, abstracts and full text for their potential inclusion against the eligibility criteria. Any disagreement was resolved by discussion with a third reviewer. In instances where there was limited or incomplete information regarding a study’s eligibility (e.g. when only an abstract was available), the study authors were contacted to request the full text or further details.
Data extraction, coding and analysis
One author collected data from all included articles using a pre-tested form; a second author collected data from a 50% sample of the articles.
Data collected on the characteristics of included studies
We collected data about the following: (i) the type of articles (coded as per our inclusion criteria), (ii) the main contribution(s) of the article (e.g. critique of methods), (iii) a precis of the methods or approaches described and (iv) the data on which the article was based (e.g. audit of methods used in a sample of overviews, author’s experience).
Coding and analysis to develop the framework of methods
We coded the extent to which each article described methods or approaches pertaining to each step of an overview (i.e. mentioned without description, described—insufficient detail to implement, described—implementable). The subset of articles coded as providing description were read by two authors (CL, SB or JM) who independently drafted the framework for that step to capture and categorise all available methods. We grouped conceptually similar approaches together and extracted examples to illustrate the options. Groups were labelled to delineate the unique decision points faced when planning each step of an overview (e.g. determine how to deal with discordance across systematic review (SR)/meta-analyses (MAs) and determine criteria for selecting SR/MAs, where SR/MAs include overlapping studies). To ensure comprehensiveness of the framework, methods were inferred when a clear alternative existed to a reported method (e.g. using tabular or graphical approaches to present discordance (6.2, Table 4)). The drafts and multiple iterations of the framework for each step were discussed and refined by all authors.
Stage II: identification and mapping of evaluations of methods
In addition to the main searches outlined in the ‘Search methods’ section for Stage I, we planned to undertake purposive searches to locate ‘studies evaluating methods’ where the main searches were unlikely to have located these evaluations. For this second paper, we undertook a purposive search to locate studies evaluating assessment of risk of bias tools for SRs, since these studies may not have mentioned ‘overviews’ (or its synonyms) in their titles or abstracts and thus would not have been identified in the main searches. However, through our main search, we identified a SR that had examined quality assessment or critical appraisal tools for assessing SRs or meta-analyses . We therefore did not develop a new purposive search strategy, but instead used the strategy in the SR, and ran it over the period January 2013—August 2016 to locate studies published subsequent to the SR (Additional file 2). For the other steps, the identified methods were specific to overviews, so evaluations were judged likely to be retrieved by our main searches.
To create the evidence map, we identified studies evaluating methods for overviews of systematic reviews of interventions.
SRs of methods studies that have evaluated methods for overviews
Primary methods studies that have evaluated methods for overviews
Studies published in languages other than English
Methods studies that have evaluated methods for network meta-analysis
We added the additional criterion that methods studies had to have a stated aim to evaluate methods, since our focus was on evaluation and not just application of a method.
We used the same process, as outlined in the ‘Study selection’ section, for determining which studies located from the main search met the inclusion criteria. For studies located from the purposive search, one author reviewed title, abstracts and full text for their potential inclusion against the eligibility criteria.
We extracted data from primary methods studies, or SRs of methods studies that evaluated the measurement properties of tools for assessing the risk of bias in SRs and one study that developed measures to quantify overlap of primary studies in overviews. The data extracted from these studies were based on relevant domains of the COSMIN checklist (Table 1) [13, 14]. We had originally planned to extract quantitative results from the methods evaluations relating to the primary objectives; however, on reflection, we opted not to do this since we felt this lay outside the purpose of the evidence map. Data were extracted independently by three authors (CL, SM, SB, JM).
Assessment of the risk of bias
For primary methods studies, we extracted and tabulated study characteristics that may plausibly be associated with either bias or the generalisability of findings (external validity) (Table 1). For SRs of methods studies, we used the ROBIS tool to identify concerns with the review process in the specification of study eligibility (Domain 1), methods used to identify and/or select studies (Domain 2), and the methods used to collect data and appraise studies (Domain 3) (Table 1) . We then made an overall judgement about the risk of bias arising from these concerns (low, high, or unclear). We did not assess Domain 4 of ROBIS, since this domain covers synthesis methods that are of limited applicability to the included reviews.
The yield, characteristics and description of the studies evaluating methods were described and mapped to the framework of methods.
Results of the main search
Details of our search results are reported in our first companion paper . Here, we note the results from the additional purposive search and changes in search results between the papers. Our main search strategy retrieved 1179 unique records through searching databases, methods collections and other sources (Fig. 3) . After screening abstracts and full text, 66 studies remained, 42 of which were included in stage I and 24 studies in stage II (exclusions found in Additional file 3). Our purposive search to identify studies evaluating tools for assessing the risk of bias in SRs (rather than primary studies) found no further stage II studies (see Additional file 4 for flowchart).
Of the 24 included stage II studies, 12 evaluated search filters for SRs (reported in paper 1 ), 11 evaluated risk of bias assessment tools for SRs, and one evaluated a synthesis method. Of the 11 studies evaluating risk of bias assessment tools for SRs, four were SRs of methods studies ([12, 16,17,18] and seven were primary evaluation studies [15, 17, 19,20,21,22,23].
Four of the seven primary evaluations of risk of bias assessment tools [20,21,22,23] and one SR  were included in the results of the 2013 SR by Whiting  and so were not considered individually in this paper. We excluded one of the SRs since, after close examination, it became clear that it reviewed studies that applied rather than evaluated AMSTAR (A Measurement Tool to Assess Systematic Reviews [22, 23]) and so did not meet our stage II inclusion criteria . Therefore, of the 24 initially eligible stage II studies, 18 met the inclusion criteria, six of which are included in this second paper (Fig. 3).
Stage I: development and population of the framework of methods
We first describe the characteristics of the included stage I articles (see ‘Characteristics of stage I articles’; Table 2) followed by presentation of the developed framework. This presentation is organised into sections representing the main (latter) steps in conducting an overview—‘assessment of risk of bias in SRs and primary studies’, ‘synthesis, presentation and summary of findings’ and the ‘assessment of certainty of the evidence arising from the overview’. In each section, we orient readers to the structure of the methods framework, which includes a set of steps and sub-steps (which are numbered in the text and tables). Reporting considerations for all steps are reported in Additional file 5.
We focus our description on methods/options that are distinct; have added complexity, compared with SRs of primary studies; or have been proposed to deal with major challenges in undertaking an overview. Importantly, the methods/approaches and options reflect the ideas presented in the literature and should not be interpreted as endorsement for the use of the methods. We also highlight methods that may be considered for dealing with commonly encountered scenarios for which overview authors need to plan (see ‘Addressing common scenarios unique to overviews’; Table 6).
Characteristics of stage I articles
The characteristics and the extent to which articles (n = 42) described methods pertaining to the latter steps in conducting an overview are indicated in Table 2. The majority of articles were published as full reports (n = 34/42; 81%). The most common type of study was an article describing methods for overviews (n = 26/42; 62%), followed by studies examining methods used in a cohort of overviews (n = 11/42; 26%), guidance documents (n = 4/42; 10%) and commentaries and editorials (n = 1/42; 2%).
Methods for the assessment of risk of bias in SRs and primary studies were most commonly mentioned or described (n = 33), followed by methods for synthesis, presentation and summary of the findings (n = 30), and methods for the assessment of certainty of the evidence in overviews (n = 24). Few articles described methods across all of the latter steps in conducting an overview (n = 6 [1, 4, 6, 24,25,26]).
Assessment of risk of bias in SRs and primary studies
The three steps in the framework under ‘assessment of risk of bias in SRs and primary studies’ were ‘plan to assess risk of bias (RoB) in the included SRs (1.0)’, ‘plan how the RoB of the primary studies will be assessed or re-assessed (2.0)’ and ‘plan the process for assessing RoB (3.0)’ (Table 3). Note that in the following we use the terminology ‘risk of bias’, rather than quality, since assessment of SR or primary study limitations should focus on the potential of those methods to bias findings. However, the terms quality assessment and critical appraisal are common, particularly when referring to the assessment of SR methods, and hence, our analysis includes all relevant literature irrespective of terminology. We now highlight methods/approaches and options for the first two steps since these involve decisions unique to overviews.
When determining how to assess the RoB in SRs (1.1), identified approaches included the following: selecting or adapting an existing RoB assessment tool for SRs (1.1.1, 1.1.2), developing a RoB tool customised to the overview (1.1.3), using an existing RoB assessment such as those published in Health EvidenceTM  (1.1.4) or describing the characteristics of included SRs that may be associated with bias or quality without using or developing a tool (1.1.5). More than 40 tools have been identified for appraisal of SRs , only one of which is described as a risk of bias tool (ROBIS (Risk of Bias In Systematic reviews tool) ). Other tools are described as being for critical appraisal or quality assessment. Studies have identified AMSTAR [22, 23] and the OQAQ (Overview Quality Assessment Questionnaire ) as the most commonly used tools in overviews [3, 12]. Methods for summarising and presenting RoB assessments mirror those used in a SR of primary studies (1.2, 1.3).
Authors must also decide on how to assess the RoB of primary studies included within SRs (2.0). Two main approaches were identified: to either report the RoB assessments from the included SRs (2.1.1) or to independently assess RoB of the primary studies (2.1.3) (only the latter option applies when additional primary studies are retrieved to update or fill gaps in the coverage of existing SRs). When using the first approach, overview authors may also perform quality checks to verify assessments were done without error and consistently (2.1.2). In attempting to report RoB assessments from included SRs, overview authors may encounter missing data (e.g. incomplete reporting of assessments) or assessments that are flawed (e.g. using problematic tools). In addition, discrepancies in RoB assessments may be found when two or more SRs report an assessment of the same primary study but use different RoB tools or report discordant judgements for items or domains using the same tool. We identified multiple methods for dealing with these scenarios, most are applied at the data extraction stage (covered in Paper 1 ). Options varied according to the specific scenario, but included the following: (a) extracting all assessments, recording discrepancies; (b) extracting from one SR based on a priori criteria; (c) extracting data elements from the SR that meets pre-specified decision rules and (d) retrieving primary studies to extract missing data or reconcile discrepancies ().
Synthesis, presentation and summary of the findings
The six steps in the framework under ‘synthesis, presentation and summary of the findings’ were ‘plan the approach to summarising the SR results (1.0)’, ‘plan the approach to quantitatively synthesising the SR results (2.0)’ ‘plan to assess heterogeneity (3.0)’, ‘plan the assessment of reporting biases (4.0)’, ‘plan how to deal with overlap of primary studies included in more than one SR (5.0)’, and ‘plan how to deal with discordant results, interpretations and conclusions of SRs (6.0)’ (Table 4). As a note on terminology, we distinguish between discrepant data—meaning data from the same primary study that differs between what is reported in SRs due to error in data extraction, and discordant results, interpretation and conclusions of the results of SRs—meaning differences in results and conclusions of SRs based on the methodological decisions authors make, or different interpretations or judgments about the results.
An identified step of relevance to all overviews is determining the summary approach (1.2). This includes determining what data will be extracted and summarised from SRs and primary studies (e.g. characteristics of the included SRs (1.2.1), results of the included SRs (1.2.2), results of the included primary studies (1.2.3), RoB assessments of SRs and primary studies (1.2.4)) and what graphical approaches might be used to present the results (1.3). In overviews that include multiple SRs reporting results for the same population, comparison and outcome, criteria need to be determined as to whether all SR results/MAs are reported (1.1.1), or only a subset (1.1.2). When the former approach is chosen (1.1.1), methods for dealing with overlap of primary studies across SR results need to be considered (5.0), such as acknowledging (5.3.4), statistically quantifying (5.1) and visually examining and depicting the overlap (5.2). Choice of a subset of SR/MAs (1.1.2) may bring about simplicity in terms of summarising the SR results (since there will only be one or a few SRs included), but may lead to a loss of potentially important information through the exclusion of studies that are not overlapping with the selected SR result(s).
A related issue is that of discordance (6.0). Some overviews aim to compare results, conclusions and interpretations across a set of SRs that address similar questions. These overviews typically address a focused clinical question (e.g. comparing only two interventions for a specific condition and population). Identified methods included approaches to examine and record discordance (6.1.1) and the use of tools (e.g. Jadad ) or decision rules to aid in the selection of one SR/MA (6.1.2).
In addition to determining the summary approach of SR results, consideration may also be given to undertaking a new quantitative synthesis of SR results (2.0). A range of triggers that may lead to a new quantitative synthesis were identified (2.2) (e.g. incorporation of additional primary studies (2.2.2), need to use new or more appropriate meta-analysis methods (2.2.3), concerns regarding the trustworthiness of the SR/MA results (2.2.5)). When undertaking a new meta-analysis in an overview, a decision that is unique to overviews is whether to undertake a first-order meta-analysis of effect estimates from primary studies (2.3.1), or a second-order meta-analysis of meta-analysis effect estimates from the SRs (2.3.2). If undertaking a second-order meta-analysis, methods may be required for dealing with primary studies contributing data to multiple meta-analyses (5.3.2). A second-order subgroup analysis was identified as a potential method for investigating whether characteristics at the level of the meta-analysis (e.g. SR quality) modify the magnitude of intervention effect (3.3.2). If new meta-analyses are undertaken, decisions regarding the model and estimation method are required (2.5, 3.4).
Investigation of reporting biases may be done through summarising the reported investigations of reporting biases in the constituent SRs (1.2.6), or through new investigations (4.0). Overviews also provide an opportunity to identify missing primary studies through non-statistical approaches (4.2), such as comparing the included studies across SRs. An additional consideration in overviews is investigation of missing SRs. Identified non-statistical approaches to identify missing SRs included searching SR registries and protocols (4.1).
Assessment of the certainty of the evidence arising from the overview
The two steps in the framework under ‘assessment of the certainty of the evidence arising from the overview’ are as follows: ‘plan to assess certainty of the evidence (1.0)’ and ‘plan the process for assessing the certainty of the evidence (2.0)’ (Table 5). GRADE is the most widely used method for assessing the certainty of evidence in a systematic review of primary studies. The methods involve assessing study limitations (RoB, imprecision, inconsistency, indirectness, and publication bias) to provide an overall rating of the certainty of (or confidence in) results for each comparison . In an overview, planning how to assess certainty (1.1) involves additional considerations. These include deciding how to account for limitations of the included SRs (e.g. bias arising from the SR process, whether SRs directly address the overview question) and how to deal with missing or discordant data needed to assess certainty (e.g. non-reporting of heterogeneity statistics needed to assess consistency, SRs that report conflicting RoB assessments for the same study). One approach is to assess certainty of the evidence using a method designed for overviews (1.1.1). However, GRADE methods (or equivalent) have not yet been adapted for overviews and guidance on addressing issues is not available. In the absence of agreed guidance for overviews, another option is to assess the certainty of the evidence using an ad hoc method (1.1.2). For example, Pollock 2015 incorporated the limitations of included SRs in their GRADE assessment by rating down the certainty of evidence for SRs that did not meet criteria deemed to indicate important sources of bias [31, 32].
Other identified approaches use methods developed for SRs of primary studies, without adaptation for overviews. The simplest of these is to ‘report assessments of certainty of the evidence from the included SRs’ with or without checking accuracy first (1.1.3 and 1.1.4). Authors may then use approaches specified in the data extraction step to deal with missing or discrepant assessments (see paper 1 ). These approaches include simply noting missing data and discrepant assessments, or reporting assessments of certainty from an SR that meets pre-specified methodological eligibility criteria, for example, the review that addressed the overview question most directly or assessed to be at lowest risk of bias. The final option when using methods developed for SRs of primary studies involves completing the assessment of certainty from scratch (1.1.5). This option may apply in circumstances where (a) an assessment was not reported in included SRs, (b) new primary studies were retrieved that were not included in the SRs or relevant studies were not integrated into the assessment reported in the SR, (c) included SRs used different tools to assess certainty (e.g. GRADE  and the Agency for Healthcare Research and Quality’s [AHRQ] tool ) or (d) assessments are judged to be flawed or inappropriate for the overview question.
Addressing common scenarios unique to overviews
In our examination of the literature, methods were often proposed in the context of overcoming common methodological scenarios. Table 6 lists the methods options from the framework that could be used to address each scenario.
While the literature reviewed often suggested a single method or step at which a scenario should be dealt with, Table 6 shows that there are multiple options, some of which can be combined. Only those methods that provide direct solutions are listed, not those that need to be implemented as a consequence of the chosen solution. Taking an example, a commonly cited approach for dealing with reviews with overlapping primary studies is to specify eligibility criteria (or decision rules) to select one SR (see Paper 1 ). However, multiple methods exist for addressing overlap at later steps of the overview. During synthesis, for example, authors can (i) use decision rules to select one (or a subset) of meta-analyses with overlapping studies (5.3.1), (ii) use statistical approaches to deal with overlap (5.3.2), (iii) ignore overlap (5.3.3) or (iv) acknowledge overlap as a limitation (5.3.4; Table 4). Alternatively, overlap may be addressed when assessing certainty of the evidence. Any of these approaches can be combined with methods to quantify and visually present overlap (5.1–5.2; Table 4).
Stage II: identification and mapping of evaluations of methods
Mapping studies evaluating methods to the framework
Five studies, published between 2011 and 2015, evaluated tools to assess risk of bias in SRs. Two were SRs [12, 17] and three were primary studies not included in either of the SRs [15, 19, 34]. Characteristics of these studies are summarised in Tables 7 and 8. All five studies map to the sub-option ‘select an existing RoB assessment tool for SRs’ (1.1.1) of the approach ‘plan to assess RoB in the included SRs’ (1.0) under the ‘assessment of RoB in SRs and primary studies’ step of the framework (see ‘Assessment of risk of bias in SRs and primary studies’; Table 3).
We found one study that evaluated methods for synthesis. Pieper 2014b developed and validated two measures to quantify the degree of overlap in primary studies across multiple SRs . This study maps to the ‘synthesis, presentation and summary of the findings’ step of the framework (see ‘Synthesis, presentation and summary of the findings’; Table 4) in option 5.0 ‘plan how to deal with overlap of primary studies included in more than one SR’.
We found no stage II studies evaluating methods in the ‘assessment of the certainty of evidence arising from the overview’ step of the framework (Table 5).
Two SRs reviewed published tools to assess the risk of bias in SRs [12, 17]. Pieper  reviewed evidence of the reliability and construct validity of the AMSTAR [22, 23] and R-AMSTAR (revised-AMSTAR ) tools. Whiting  reviewed the content and measurement properties of 40 critical appraisal tools (Table 7). The review includes a summary of tool content (items and domains measured), tool structure (e.g. checklist, domain based), and item rating (i.e. response options). Studies included in Whiting  reported methods of development for 17 of 40 tools (i.e. providing information needed to assess content validity). Three of these 17 tools were judged to have been developed using a ‘rigorous’ process (notably AMSTAR [22, 23, 37], Higgins , and OQAQ ) (details in Table 7). Inter-rater reliability assessments were available from 11 of 13 studies included in Pieper , and for five of the 40 tools (most reporting kappa or intraclass correlation coefficient) in Whiting . Six of the studies included in Pieper  assessed construct validity. No tests of validity were reported for any of the tools in Whiting  (although exploratory factor analysis was used to develop the content of AMSTAR). In addition, Pieper  reported data on the time to complete the assessment of each tool.
Of the three primary studies that evaluated RoB tools, two assessed the reliability and validity of AMSTAR and OQAQ [19, 34], one assessed the reliability and validity of the Rapid Appraisal Protocol internet Database (RAPiD) and the Quality and Applicability of Systematic Reviews of the National Center for the Dissemination of Rehabilitation Research (NCDRR) , and one reported the development and reliability of ROBIS  (Table 8). In addition, two of the three studies assessed the time to complete assessments [19, 34].
Assessment of risk of bias in studies evaluating methods
Both SRs [12, 17] were judged at low risk of bias, based on assessment using the ROBIS tool. Assessments for each domain are reported in Table 7. Of the four primary studies evaluating methods [15, 19, 34, 35]: (i) none referred to a study protocol or noted the existence of one, (ii) three used convenience samples as a method to select the sample of SRs to which the tool/measure was applied, (iii) the three studies that evaluated RoB tools either used a convenience sample, or provided no description, of the process for selecting raters who applied the tool and (iv) only one pre-specified hypotheses for testing of the validity of the measure  (Table 8).
In this paper, we present our developed framework of overview methods for the final steps in conducting an overview—assessment of the risk of bias in SRs and primary studies; synthesis, presentation and summary of the findings; and assessment of the certainty of evidence arising from the overview. We identified five stage II evaluation studies that mapped to the ‘assessment of the risk of bias in SRs and primary studies’ step of the framework and one study that mapped to the ‘synthesis, presentation and summary of the findings’ step. The evaluations included psychometric testing of tools to assess the risk of bias in SRs and development of a statistical measure to quantify overlap in primary studies across SRs. Results presented in this paper, in combination with our companion paper , provide a framework—the MOoR framework—of overview methods for all steps in the conduct of an overview. The framework makes explicit the large number of steps and methods that need to be considered when planning an overview and the unique decisions that need to be made as compared with a SR of primary studies. Here, we focus on issues pertinent to this second companion paper and present some overarching considerations.
What this study adds to guidance and knowledge about overview methods
A key observation from our first paper, and aligned with conclusions of others [8, 9], was that there are important gaps in the guidance on the conduct of overviews . Similar conclusions can be drawn from this paper, wherein guidance covers particular options, but not alternatives, and there is a lack of operational guidance for many methods. This is particularly pertinent for the step ‘assessment of the certainty of the evidence arising from the overview’, where GRADE methods (or equivalent) have yet to be developed for overviews. An exception was within the ‘assessment of risk of bias in SRs and primary studies’ step, where many tools for appraising or assessing the risk of bias in SRs have been developed, with psychometric evaluation for some tools, yielding at least some empirical evidence to underpin selection of tools. Detailed guidance on the applications of these tools has also been published.
The framework extends previous guidance on overviews methods [4, 39] through provision of a range of methods and options that might be used for each step. For most methods, we identified a lack of evaluation studies, indicating that there is limited evidence to inform methods decision-making in overviews. However, not all methods presented necessarily require evaluation. Theoretical considerations or poor face (or content) validity of a method may determine that it should not be used. For example, in the ‘assessment of risk of bias in SRs and primary studies’ step, an identified option (and one that has been used in some overviews) is to not report or assess RoB in the primary studies (2.1.4). Since the interpretation of evidence is highly dependent on limitations of primary studies within an SR, this option has little face validity.
A further extension to previous guidance is the linking of methods from our framework to address commonly arising challenges in overviews. This linking demonstrates that multiple methods are available for addressing each scenario, as illustrated in ‘Addressing common scenarios unique to overviews’ section using the example of the range of methods available for dealing with reviews that include overlapping primary studies.
Strengths and limitations
The strengths and limitations described in the first paper in this series  are now briefly described here. The strengths of our research included (a) noting any deviations to our planned protocol , (b) using consistent language throughout the framework and an intuitive organising structure to group related methods and (c) drafting of the framework for each step by two authors independently. The limitations included the following: (a) the subjective nature of the research involving ‘translating’ descriptions of methods into a common language or standardised phrasing, (b) exclusion of articles that could have been of relevance to overviews (e.g. methods of indirect comparison and updating systematic reviews) and (c) difficulty in retrieving methods studies as methods collections are not routinely updated (for example, the Cochrane Methodology Register has not been updated since July 2012 ; and the Scientific Resource Center Methods library’s most recent article is from 2013).
An additional limitation is that new methods and methods evaluations may have been published since our last search (August 2016). However, we sought to identify methods that were missing from the literature (through inference) so the structure of the framework is unlikely to change. Given the sparsity of evidence about the performance of methods, any new evaluations will be an important addition to the evidence base but are unlikely to provide definitive evidence. One recent example is the publication of AMSTAR 2 . While the development of AMSTAR 2 reflects an important advancement on the previous version of AMSTAR (extending to non-randomised studies and changing the response format), the tool will require application and further testing in overviews before its measurement properties can be fully established and compared to existing tools.
Future research to refine and populate the framework and evidence map
Overview methods are evolving, and as methods are developed and evaluated, the evidence map can be further refined and populated. There are two related, but distinct streams of research here. The first stream relates to the development and application of methods. Substantial work is needed to provide detailed guidance for applying methods that have been advocated for use in overviews, in addition to developing new methods where gaps exist. The development of GRADE guidance for overviews is an important example where both methods development and detailed guidance is required.
The second stream of research involves methods evaluation. In our first paper, we suggested three domains against which the performance of overview methods should be evaluated: the validity and reliability of overview findings, the time and resources required to complete the overview, and the utility of the overview for decision-makers. For example, researchers could compare the statistical performance of different metrics to assess the degree of overlap, or different statistical methods to adjust for overlap in meta-analyses, using numerical simulation studies. A further area of research could include evaluation of different visual presentations of the range of summary results extracted from the constituent SRs. The framework will need to be refined, in response to methods development and evaluation. As mentioned in Paper 1, visual representation of an evidence map of overview methods will be useful when more evidence is available.
Furthermore, our framework and evidence map only focused on overviews of intervention reviews. The framework and evidence map could be extended to include methods for other types of overviews, such as overviews of diagnostic test accuracy reviews or prognostic reviews .
A framework of methods for the final steps in conducting, interpreting and reporting overviews was developed, which in combination with our companion paper, provide a framework of overview methods—the MOoR framework—for all steps in the conduct of an overview. Evaluations of methods for overviews were identified and mapped to the framework. Many methods have been described for use in the latter steps in conducting an overview; however, evaluation and guidance for applying these methods is sparse. The exception is RoB assessment, for which a multitude of tools exist—several with sufficient evaluation and guidance to recommend their use. Evaluation of other methods is required to provide a comprehensive evidence map.
Further evaluation of methods for overviews will facilitate more informed methods decision-making. Results of this research may be used to identify and prioritise methods research, aid authors in the development of overview protocols and offer a basis for the development of reporting checklists.
- AHRQ’s EPC:
Agency for Healthcare Research and Quality s Evidence-based Practice Center
A Measurement Tool to Assess Systematic Reviews
Assessing the Quality and Applicability of Systematic Reviews
Corrected Covered Area
Cochrane Database of Systematic Reviews
Comparing Multiple Interventions Methods Group
Heath technology assessment
Joanna Briggs Institute
Methodological Expectations of Cochrane Intervention Reviews
Quality and Applicability of Systematic Reviews of the National Center for the Dissemination of Rehabilitation Research
Overview Quality Assessment Questionnaire
Population (P), intervention (I), comparison (C) and outcome (O)
International Prospective Register of Systematic Reviews
Rapid Appraisal Protocol internet Database
Randomised controlled trial
Risk of bias
Risk of Bias In Systematic reviews
Caird J, Sutcliffe K, Kwan I, Dickson K, Thomas J. Mediating policy-relevant evidence at speed: are systematic reviews of systematic reviews a useful approach? Evid Policy. 2015;11:81–97.
Lunny C, McKenzie JE, McDonald S. Retrieval of overviews of systematic reviews in MEDLINE was improved by the development of an objectively derived and validated search strategy. J Clin Epidemiol. 2016;74:107–18.
Pieper D, Buechter R, Jerinic P, Eikermann M. Overviews of reviews often have limited rigor: a systematic review. J Clin Epidemiol. 2012;65:1267–73.
Becker LA, Oxman AD. Chapter 22: Overviews of reviews. In: JPT H, Green SE, editors. Cochrane Handbook for Systematic Reviews of Interventions. Hoboken: Wiley; 2008. p. 607–31.
Bolland MJ, Grey A, Reid IR. Differences in overlapping meta-analyses of vitamin D supplements and falls. J Clin Endocrinol Metab. 2014;99:4265–72.
Cooper H, Koenka AC. The overview of reviews: unique challenges and opportunities when research syntheses are the principal elements of new integrative scholarship. Am Psychol. 2012;67:446–62.
McKenzie JE, Brennan SE. Overviews of systematic reviews: great promise, greater challenge. Syst Rev. 2017;6:185.
Ballard M, Montgomery P. Risk of bias in overviews of reviews: a scoping review of methodological guidance and four-item checklist. Res Synth Methods. 2017;8:92–108.
Pollock M, Fernandes RM, Becker LA, Featherstone R, Hartling L. What guidance is available for researchers conducting overviews of reviews of healthcare interventions? A scoping review and qualitative metasummary. Syst Rev. 2016;5:190.
Lunny C, Brennan SE, McDonald S, McKenzie JE. Toward a comprehensive evidence map of overview of systematic review methods: paper 1-purpose, eligibility, search and data extraction. Syst Rev. 2017;6:231.
Lunny C, Brennan SE, McDonald S, McKenzie JE. Evidence map of studies evaluating methods for conducting, interpreting and reporting overviews of systematic reviews of interventions: rationale and design. Syst Rev. 2016;5:4.
Whiting P, Davies P, Savović J, Caldwell D, Churchill R. Chapter 4. Phase 2: review of existing quality assessment tools for systematic reviews. Evidence to inform the development of ROBIS, a new tool to assess the risk of bias in systematic reviews, Available from http://www.robis-tool.info [accessed 20/11/2017]; 2013. p. 22–35.
Mokkink LB, Terwee CB, Gibbons E, Stratford PW, Alonso J, Patrick DL, Knol DL, Bouter LM, de Vet HC. Inter-rater agreement and reliability of the COSMIN (COnsensus-based Standards for the selection of health status Measurement Instruments) checklist. BMC Med Res Methodol. 2010;10:82.
Mokkink LB, Terwee CB, Stratford PW, Alonso J, Patrick DL, Riphagen I, Knol DL, Bouter LM, de Vet HC. Evaluation of the methodological quality of systematic reviews of health status measurement instruments. Qual Life Res. 2009;18:313–33.
Whiting P, Savović J, Higgins JPT, Caldwell DM, Reeves BC, Shea B, Davies P, Kleijnen J, Churchill R, group R. ROBIS: a new tool to assess risk of bias in systematic reviews was developed. J Clin Epidemiol. 2016;69:225–34.
Bai A, Shukla VK, Bak G, Wells G. Chapter 4: tools selected through QAT project. In: quality assessment tools project report. Ottawa: Canadian Agency for Drugs and Technologies in Health; 2012.
Pieper D, Buechter RB, Li L, Prediger B, Eikermann M. Systematic review found AMSTAR, but not R (evised)-AMSTAR, to have good measurement properties. J Clin Epidemiol. 2014;
Whiting P, Davies, P., Savović, J., Caldwell, D., Churchill, R.: Chapter 5. Phase 3: review of studies that have used the AMSTAR tool. Evidence to inform the development of ROBIS, a new tool to assess the risk of bias in systematic reviews, Available from http://www.robis-tool.info [accessed 20/11/2017]. 2013.
Parmelli E, Banzi R, Fernandez Del Rio MDP, Minozzi S, Moja L, Pecoraro V, Liberati A: Using AMSTAR to assess the methodological quality of systematic reviews: an external validation study. Poster presentation at the 19th Cochrane Colloquium; 2011 Oct 19-22; Madrid, Spain [abstract]. In Cochrane Database Syst Rev, Supplement, vol. Suppl. pp. 139; 2011:139.
Popovich I, Windsor B, Jordan V, Showell M, Shea B, Farquhar CM. Methodological quality of systematic reviews in subfertility: a comparison of two different approaches. PLoS ONE. 2012;7:e50403.
Schmitter M, Sterzenbach G, Faggion CM Jr, Krastl G. A flood tide of systematic reviews on endodontic posts: methodological assessment using of R-AMSTAR. Clin Oral Investig. 2013;17:1287–94.
Shea BJ, Grimshaw JM, Wells GA, Boers M, Andersson N, Hamel C, Porter AC, Tugwell P, Moher D, Bouter LM. Development of AMSTAR: a measurement tool to assess the methodological quality of systematic reviews. BMC Med Res Methodol. 2007;7:10.
Shea BJ, Hamel C, Wells GA, Bouter LM, Kristjansson E, Grimshaw J, Henry DA, Boers M. AMSTAR is a reliable and valid measurement tool to assess the methodological quality of systematic reviews. J Clin Epidemiol. 2009;62:1013–20.
Robinson KA, Chou R, Berkman ND, Newberry SJ, Fu R, Hartling L, Dryden D, Butler M, Foisy M, Anderson J, et al. Twelve recommendations for integrating existing systematic reviews into new reviews: EPC guidance. J Clin Epidemiol. 2016;70:38–44.
Ryan RE, Kaufman CA, Hill SJ. Building blocks for meta-synthesis: data integration tables for summarising, mapping, and synthesising evidence on interventions for communicating with health consumers. BMC Med Res Methodol. 2009;9:16.
Thomson D, Russell K, Becker L, Klassen TP, Hartling L. The evolution of a new publication type: steps and challenges of producing overviews of reviews. Res Syn Method. 2010;1:198–211.
Dobbins M. Health Evidence (TM): a public health knowledge repository disseminating evidence to decision makers. Euro J Public Health. 2016;26:363. Available at: https://www.healthevidence.org
Oxman AD, Guyatt GH. Validation of an index of the quality of review articles. J Clin Epidemiol. 1991;44:1271–8.
Jadad AR, Cook DJ, Browman GP. A guide to interpreting discordant systematic reviews. Cmaj. 1997;156:1411–6.
Guyatt GH, Oxman AD, Vist GE, Kunz R, Falck-Ytter Y, Alonso-Coello P, Schunemann HJ. GRADE: an emerging consensus on rating quality of evidence and strength of recommendations. Bmj. 2008;336:924–6.
Pollock A, Farmer SE, Brady MC, Langhorne P, Mead GE, Mehrholz J, van Wijck F, Wiffen PJ. An algorithm was developed to assign GRADE levels of evidence to comparisons within systematic reviews. J Clin Epidemiol. 2015;
Murad MH, Mustafa R, Morgan R, Sultan S, Falck-Ytter Y, Dahm P. Rating the quality of evidence is by necessity a matter of judgment. J Clin Epidemiol. 2016;74:237–8.
Berkman ND, Lohr KN, Ansari MT, Balk EM, Kane R, McDonagh M, Morton SC, Viswanathan M, Bass EB, Butler M, et al. Grading the strength of a body of evidence when assessing health care interventions: an EPC update. J Clin Epidemiol. 2015;68:1312–24.
Pieper D, Mathes T, Eikermann M. Impact of choice of quality appraisal tool for systematic reviews in overviews. J Evid Based Med. 2014;7:72–8.
Pieper D, Antoine SL, Mathes T, Neugebauer EA, Eikermann M. Systematic review finds overlapping reviews were not mentioned in every other overview. J Clin Epidemiol. 2014;67:368–75.
Kung J, Chiappelli F, Cajulis OO, Avezova R, Kossan G, Chew L, et al. From systematic reviews to clinical recommendations for evidence-based health care: validation of revised assessment of multiple systematic reviews (R-AMSTAR) for grading of clinical relevance. Open Dent J. 2010;4:4–91.
Shea BJ, Bouter LM, Peterson J, Boers M, Andersson N, Ortiz Z, Ramsay T, Bai A, Shukla VK, Grimshaw JM. External validation of a measurement tool to assess systematic reviews (AMSTAR). PLoS One. 2007;2:e1350.
Higgins JPT, Lane PW, Anagnostelis B, Anzures-Cabrera J, Baker NF, Cappelleri JC, Haughie S, Hollis S, Lewis SC, Moneuse P, Whitehead A. A tool to assess the quality of a meta-analysis. Res Synth Methods. 2013;4:351–66.
Joanna Briggs Institute. Methodology for JBI Umbrella Reviews. South Australia: The University of Adelaide; 2014.
Cochrane Methods Group. About the Cochrane Methodology Register: Cochrane; 2012. http://www.cochranelibrary.com/help/the-cochrane-methodology-register-july-issue-2012.html
Shea BJ, Reeves BC, Wells G, Thuku M, Hamel C, Moran J, Moher D, Tugwell P, Welch V, Kristjansson E, Henry DA. AMSTAR 2: a critical appraisal tool for systematic reviews that include randomised or non-randomised studies of healthcare interventions, or both. BMJ. 2017;358:j4008.
Hunt H, Pollock A, Campbell P, Estcourt L, Brunton G. An introduction to overviews of reviews: planning a relevant research question and objective for an overview. Syst Rev. 2018;7:39.
Baker PRA, Costello JT, Dobbins M, Waters EB. The benefits and challenges of conducting an overview of systematic reviews in public health: a focus on physical activity. J Publ Health. 2014;36:517–21.
Brunton G, Thomas J, Paraskeva N, Caird J, Rumsey N. Putting the issues on the table: summarising outcomes from reviews of reviews to inform health policy. In: Cochrane Colloquium. Québec City; 2006.
Büchter R, Pieper D. How do authors of Cochrane Overviews deal with conflicts of interest relating to their own systematic reviews? In: Cochrane Colloquium. Vienna; 2015.
Chen YF, Hemming K, Chilton PJ, Gupta KK, Altman DG, Lilford RJ. Scientific hypotheses can be tested by comparing the effects of one treatment over many diseases in a systematic review. J Clin Epidemiol. 2014;67:1309–19.
CMIMG C: Review Type & Methodological Considerations --Background Paper for the First Part of the Paris CMIMG Discussion. 2012.
Crick K, Wingert A, Williams K, Fernandes RM, Thomson D, Hartling L. An evaluation of harvest plots to display results of meta-analyses in overviews of reviews: a cross-sectional study. BMC Med Res Methodol. 2015;15:91.
Flodgren G, Shepperd S, Eccles M. Challenges facing reviewers preparing overviews of reviews (P2A194). In: Cochrane Colloquium. Madrid; 2011.
Foisy M, Becker LA, Chalmers JR, Boyle RJ, Simpson EL, Williams HC. Mixing with the ‘unclean’: including non-Cochrane reviews alongside Cochrane reviews in overviews of reviews (P2A157). In: Cochrane Colloquium. Madrid; 2011.
Foisy MFR, Dryden DM, Hartling L. Grading the quality of evidence in existing systematic reviews: challenges and considerations. In: 22nd Cochrane Colloquium. Hyderabad: Wiley; 2014.
Foisy M, Hartling L. Challenges and considerations involved in using AMSTAR in overviews of reviews. In: Cochrane Colloquium. Hyderabad; 2014.
Hartling L, Chisholm A, Thomson D, Dryden DM. A descriptive analysis of overviews of reviews published between 2000 and 2011. PloS one. 2012;7:e49667.
Hartling LDD, Vandermeer B, Fernandes R. Generating empirical evidence to support methods for overviews of reviews. In: Cochrane Colloquium. Quebec City; 2013.
Hartling L, Vandermeer B, Fernandes RM. Systematic reviews, overviews of reviews and comparative effectiveness reviews: a discussion of approaches to knowledge synthesis. Evid Based Child Health. 2014;9:486–94.
Hemming K, Bowater RJ, Lilford RJ. Pooling systematic reviews of systematic reviews: a Bayesian panoramic meta-analysis. Stat Med. 2012;31:201–16.
Ioannidis JPA. Integration of evidence from multiple meta-analyses: a primer on umbrella reviews, treatment networks and multiple treatments meta-analyses. CMAJ. 2009;181:488–93.
James BM, Baker PRA, Costello JT, Francis DP. Informing methods for preparing public health overviews of reviews: a comparison of public health overviews with Cochrane Overviews published between 1999 and 2014. In: Cochrane Colloquium. Hyderabad; 2014.
Aromataris E, Fernandez R, Godfrey CM, Holly C, Khalil H, Tungpunkom P. Summarizing systematic reviews: methodological development, conduct and reporting of an umbrella review approach. Int J Evid Based Healthc. 2015;13:132–40.
Kovacs FM, Urrutia G, Alarcon JD. “Overviews” should meet the methodological standards of systematic reviews. Eur Spine J. 2014;23:480.
Kramer S, Langendam M, Elbers R, Scholten R, Hooft L. Preparing an overview of reviews: lessons learned. Poster. In: Cochrane Colloquium; 2009 Oct 11-14. Singapore; 2009.
Li LM, Tian JT, Tian H, Sun R, Liu Y, Yang K. Quality and transparency of overviews of systematic reviews. J Evid-Based Med. 2012;5:166–73.
Moja L, Fernandez del Rio MP, Banzi R, Cusi C, D'Amico R, Liberati A, Lodi G, Lucenteforte E, Minozzi S, Pecoraro V, et al. Multiple systematic reviews: methods for assessing discordances of results. Intern Emerg Med. 2012;7:563–8.
O'Mara AJ, Jamal F, Parry W, Lorenc T, Cooper C. Guidelines for conducting and reporting reviews of reviews: dealing with topic relevances and double-counting. Poster presentation at the 19th Cochrane Colloquium; 2011 Oct 19-22; Madrid, Spain [abstract]. In Cochrane Database Syst Rev, Supplement, issue CD000003. 2011. p. 101. Available at: https://cmr.cochrane.org/?CRGReportID=16702.
Büchter R, Pieper D, Jerinic P. Overviews of systematic reviews often do not assess methodological quality of included reviews. Poster. In: 19th Cochrane Colloquium, vol. Suppl. Madrid: Cochrane Database Syst Rev; 2011. p. 105–6.
Pieper DA, Morfeld S-L, Mathes J-C, Mathes T, Eikermann M. Methodological approaches in conducting overviews: current state in HTA agencies. Res Syn Method. 2014;5:187–99.
JPT H, Green S, editors. Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [updated March 2011]. In: : The Cochrane Collaboration. p. 2011. Available from http://handbook.cochrane.org.
Pieper D, Antoine S, Neugebauer EA, Eikermann M. Up-to-dateness of reviews is often neglected in overviews: a systematic review. J Clin Epidemiol. 2014;67:1302–8.
Robinson KA, Chou R, Berkman ND, Newberry SJ, Fu R, Hartling L, Dryden D, Butler M, Foisy M, Anderson J, Motu’apuaka ML, Relevo R, Guise JM, Chang S. Integrating bodies of evidence: existing systematic reviews and primary studies. In: Methods Guide for Effectiveness and Comparative Effectiveness Reviews. Rockville: Agency for Healthcare Research and Quality (US); 2008.
Robinson KA, Whitlock EP, O'Neil ME, Anderson JK, Hartling L, Dryden DM, Butler M, Newberry SJ, McPheeters M, Berkman ND. Integration of existing systematic reviews. In Research White Paper (Prepared by the Scientific Resource Center under Contract No 290-2012-00004-C). Rockville: Agency for Healthcare Research and Quality; 2014.
White CM, Ip S, McPheeters MC, Tim S, Chou R, Lohr KN, Robinson K, McDonald K, Whitlock EP. Using existing systematic reviews to replace de novo processes in conducting comparative effectiveness reviews. In Methods Guide for Comparative Effectiveness Reviews. Rockville: Agency for Healthcare Research and. Quality; 2009.
Whitlock EP, Lin JS, Chou R, Shekelle P, Robinson KA. Using existing systematic reviews in complex systematic reviews. Ann Intern Med. 2008;148:776–82.
Salanti G, Becker L, Caldwell D, Churchill R, Higgins J, Li T, Schmid C. Evolution of Cochrane Intervention Reviews and Overviews of Reviews to better accommodate comparisons among multiple interventions. In: Report from a meeting of the Cochrane Comparing Multiple Interventions Methods Groups: Cochrane Comparing Multiple Interventions Methods Groups; 2011.
Schmidt FL, Oh IS. Methods for second order meta-analysis and illustrative applications. Organ Behav Hum Decis Process. 2013;121:204–18.
Silva V, Grande AJ, Carvalho AP, Martimbianco AL, Riera R. Overview of systematic reviews - a new type of study. Part II. Sao Paulo Med J. 2015;133:206–17.
Singh JP. Development of the Metareview Assessment of Reporting Quality (MARQ) Checklist. Rev Fac Med Univ Nac Colomb. 2012;60:325–32.
Smith V, Devane D, Begley CM, Clarke M. Methodology in conducting a systematic review of systematic reviews of healthcare interventions. BMC Med Res Methodol. 2011;11:15.
Tang LL, Caudy M, Taxman F. A statistical method for synthesizing meta-analyses. Comput Math Methods Med. 2013;2013:732989.
Thomson D, Foisy M, Oleszczuk M, Wingert A, Chisholm A, Hartling L. Overview of reviews in child health: evidence synthesis and the knowledge base for a specific population. Evidence Based Child Health. 2013;8:3–10.
Wagner S, White M, Schultz I, Iverson R, Hsu V, McGuire L, Schultz W. Assessing a systematic review of systematic reviews: developing a criteria. In: Innovation in worker health and safety: Annual Conference, Canadian Association for Research on Work and Health, June 1-2, 2012. Vancouver; 2012. https://www.wwdpi.org/SiteCollectionDocuments/CIRPD-Research/CARWH2012/P3_MethodologicalCriteria.pdf.
McMaster University: Health systems evidence. Available from: http://www.healthsystemsevidence.org/. 2011.
Patnode CD, Henderson JT, Thompson JH, Senger CA, Fortmann SP, Whitlock EP. Behavioral counseling and pharmacotherapy interventions for tobacco cessation in adults, including pregnant women: a review of reviews for the U.S. Preventive Services Task Force. Ann Intern Med. 2015;163:608–21.
Unit PHR. Critical Appraisal Skills Programme (CASP). 10 questions to help you make sense of reviews. Retrieved from: http://www.casp-uk.net/. Oxford: Public Health Resource Unit; 2006.
FOCUS. FOCUS critical appraisal tool. London: The Royal College of Psychiatrists; 2001.
Beck CT. Use of meta-analysis as a teaching strategy in nursing research courses. J Nurs Educ. 1997;36:87–90.
(NHMRC) National Health and Medical Research Council. How to review the evidence: assessment and application of scientific evidence. http://www.nhmrc.gov.au/guidelines/publications/cp69. Canberra; 2000.
(SIGN) Scottish Intercollegiate Guidelines Network HIS, SIGN 50. Methodology checklist 1: systematic reviews and meta-analyses. Edinburgh: Scottish Intercollegiate Guidelines Network, Healthcare Improvement Scotland; 2009. Available at: http://www.sign.ac.uk/checklists-and-notes.html.
Joanna Briggs Institute. RAPid: Rapid Appraisal protocol internet database. Adelaide: The Joanna Briggs Institute; 2006.
Assendelft WJ, Koes BW, Knipschild PG, Bouter LM. The relationship between methodological quality and conclusions in reviews of spinal manipulation. JAMA. 1995;274:1942–8.
Auperin A, Pignon JP, Poynard T. Review article: critical review of meta-analyses of randomized clinical trials in hepatogastroenterology. Aliment Pharmacol Ther. 1997;11:215–25.
Crombie IK. The pocket guide to critical appraisal: a handbook for health care professionals. London: BMJ Publishing Group; 1996.
Geller NL, Proschan M. Meta-analysis of clinical trials: a consumer’s guide. J Biopharm Stat. 1996;6:377–94.
Glenny A, Esposito M, Coulthard P, Worthington H. The assessment of systematic reviews in dentistry. Eur J Oral Sci. 2003;111:85–92.
Greenhalgh T. Papers that summarise other papers (systematic reviews and meta-analyses). Bmj. 1997;315:672–5.
Ho RC, Ong HS, Kudva KG, Cheung MW, Mak A. How to critically appraise and apply meta-analyses in clinical practice. Int J Rheum Dis. 2010;13:294–9.
Irwig L, Tosteson AN, Gatsonis C, Lau J, Colditz G, Chalmers TC, Mosteller F. Guidelines for meta-analyses evaluating diagnostic tests. Ann Intern Med. 1994;120:667–76.
Knox EM, Thangaratinam S, Kilby MD, Khan KS. A review of the methodological features of systematic reviews in fetal medicine. Eur J Obstet Gynecol Reprod Biol. 2009;146:121–8.
Li T, Vedula SS, Scherer R, Dickersin K. What comparative effectiveness research is needed? A framework for using guidelines and systematic reviews to identify evidence gaps and research priorities. Ann Intern Med. 2012;156:367–77.
Light RJ, Pillemer DB. The science of reviewing research. Cambridge: Harvard University Press; 1984.
Lundh A, Sismondo S, Lexchin J, Busuioc O, Bero L. Industry sponsorship and research outcome. Cochrane Database Syst Rev. 2015;12
Mailis A, Taenzer P. Evidence-based guideline for neuropathic pain interventional treatments: spinal cord stimulation, intravenous infusions, epidural injections and nerve blocks. Pain Res Manag. 2012;17:150–8.
Minelli C, Thompson JR, Abrams KR, Thakkinstian A, Attia J. The quality of meta-analyses of genetic association studies: a review with recommendations. Am J Epidemiol. 2009;170:1333–43.
Mulrow CD. The medical review article: state of the science. Ann Intern Med. 1987;106:485–8.
Nony P, Cucherat M, Haugh MC, Boissel JP. Critical reading of the meta-analysis of clinical trials. Therapie. 1995;50:339–51.
Oxman AD, Guyatt GH. Guidelines for reading literature reviews. Cmaj. 1988;138:697–703.
Oxman AD, Cook DJ, Guyatt GH. Users’ guides to the medical literature. VI. How to use an overview. Evidence-Based Medicine Working Group. JAMA. 1994;272:1367–71.
Oxman AD. Checklists for review articles. BMJ. 1994;309:648–51.
Philibert A, Loyce C, Makowski D. Assessment of the quality of meta-analysis in agronomy. Agric Ecosyst Environ. 2012;148:72–82.
Sacks HS, Berrier J, Reitman D, Ancona-Berk V, Chalmers TC. Meta-analyses of randomized controlled trials. N Engl J Med. 1987;316:450–5.
Santaguida P, Oremus M, Walker K, Wishart LR, Siegel KL, Raina P. Systematic reviews identify important methodological flaws in stroke rehabilitation therapy primary studies: review of reviews. J Clin Epidemiol. 2012;65:358–67.
Shamliyan T, Kane RL, Jansen S. Quality of systematic reviews of observational nontherapeutic studies. Prev Chronic Dis. 2010;7:A133.
Sheikh L, Johnston S, Thangaratinam S, Kilby MD, Khan KS. A review of the methodological features of systematic reviews in maternal medicine. BMC Med. 2007;5:10.
Smith AF. An analysis of review articles published in four anaesthesia journals. Can J Anaesth. 1997;44:405–9.
Thacker SB, Peterson HB, Stroup DF. Metaanalysis for the obstetrician-gynecologist. Am J Obstet Gynecol. 1996;174:1403–7.
Wilson A, Henry DA. Meta-analysis. Part 2: assessing the quality of published meta-analyses. Med J Aust. 1992;156:173-174, 177-180, 184-177.
Zambon M, Biondi-Zoccai G, Bignami E, Ruggeri L, Zangrillo A, Landoni G. A comprehensive appraisal of meta-analyses focusing on nonsurgical treatments aimed at decreasing perioperative mortality or major cardiac complications. J Anesth. 2012;26:509–15.
Task Force on Systematic Review and Guidelines. Assessing the quality and applicability of systematic reviews (AQASR). Available from http://www.ktdrr.org/aqasr. Austin: National Center for the Dissemination of Disability Research; 2011.
Higgins JPT, Lasserson T, Chandler J, Tovey D, Churchill R. Methodological Expectations of Cochrane Intervention Reviews. Cochrane: London, Version 1.05, 2018. Available at: https://community.cochrane.org/mecir-manual.
This work was conducted as part of a PhD undertaken by CL, who is funded by an Australian Postgraduate Award and an International Postgraduate Research Scholarship administered through Monash University, Australia. JEM is supported by an NHMRC Career Development Fellowship (1143429) The funding bodies were not involved in the design of the study, data collection, analysis, interpretation, preparation of the manuscript, or the decision to submit the manuscript.
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JEM is an Associate Editor of Systematic Reviews and is a Guest Editor for the thematic series ‘Overviews of systematic reviews: development and evaluation of methods’, to which this paper was submitted. SEB is an Associate Editor of Systematic Reviews. Neither JEM nor SEB were involved in the peer-review or editorial decisions for this manuscript. CL and SM declare that they have no competing interests.
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Main search strategies. (DOCX 16 kb)
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Lunny, C., Brennan, S.E., McDonald, S. et al. Toward a comprehensive evidence map of overview of systematic review methods: paper 2—risk of bias assessment; synthesis, presentation and summary of the findings; and assessment of the certainty of the evidence. Syst Rev 7, 159 (2018). https://doi.org/10.1186/s13643-018-0784-8