Table 4 Excerpts of relevant text from the literature review

Joanna Briggs Institute [27]

Umbrella review

“Conduct of an Umbrella Review offers the possibility of addressing a broad scope of issues related to a topic of interest.”

“The principal reason is to summarize evidence from many research syntheses (Becker and Oxman 2011). These may include analyses of evidence of different interventions for the same problem or condition, or evidence from more than one research synthesis investigating the same intervention and condition but addressing and reporting on different outcomes. Similarly, a researcher or reviewer may wish to summarize more than one research synthesis for different conditions, problems or populations.”

“The wide picture obtainable from the conduct of an Umbrella Review is also ideal in highlighting if the evidence base around a topic or question is consistent or if contradictory or discrepant findings exist, and in exploring and detailing the reasons why. Investigation of the evidence with an Umbrella Review allows assessment and consideration of whether reviewers addressing similar review questions independently observe similar results and arrive at generally similar conclusions.”

“…a systematic review is the main and often sole “study type” that is considered for inclusion (Becker and Oxman 2011; Hartling et al. 2012; Smith et al, 2011).”

“The principle focus of a JBI Umbrella Review is to provide a summary of existing research syntheses related to a given topic or question and not to re-synthesize, for example, the results of existing reviews or syntheses with meta-analysis or meta-synthesis.”

“…if current, multiple, good quality, systematic reviews exist about a given topic or question, any reviewer should reconsider the need to conduct yet another review addressing the same issue. Rather, these may be the basis to conduct an Umbrella Review and summarize or synthesize the findings of systematic reviews already available.”

None.

Cochrane Collaboration [9]

Overview

“Cochrane Overviews can address five different types of questions related to healthcare interventions. Specifically, they can summarize evidence from two or more systematic reviews:

• of different interventions for the same condition or population;

• that address different approaches to applying the same intervention for the same condition or population;

• of the same intervention for different conditions or populations;

• about adverse effects of an intervention for one or more conditions or populations; or

• of the same intervention for the same condition or population, where different outcomes or time points are addressed in different systematic reviews.”

“The primary reason for conducting Cochrane Overviews is that using systematic reviews as the unit of searching, inclusion, and data analysis allows authors to address research questions that are broader in scope than those examined in individual systematic reviews…a second reason for conducting a Cochrane Overview is that they may be associated with time and resource savings, since the component systematic reviews have already been conducted. A third reason for conducting a Cochrane Overview is in cases where it is important to understand the diversity present in the extant systematic review literature.”

“…it is preferable to conduct a Cochrane Review of interventions if authors anticipate the need to conduct searches for primary studies (i.e., many relevant primary studies are not included in systematic reviews) or to extract data directly from primary studies (i.e., the anticipated analyses cannot be conducted on the basis of information provided in the systematic reviews). Using primary studies as the unit of searching, inclusion and data analysis allows authors to extract all data of interest directly from the primary studies and to report these data in a standardized way. It is also preferable to conduct a Cochrane Review of interventions if authors wish to conduct network meta-analyses, which allow authors to rank order interventions and determine which work ‘best’.”

“Overviews can describe the current body of systematic review evidence on a topic of interest, or they can address a new review question that wasn’t a focus in the included systematic reviews.”

“There are several instances where authors should not conduct a Cochrane Overview. Overviews do not aim to:

• repeat or update the searches or eligibility assessment of the included systematic reviews;

• conduct a study-level search for primary studies not included in any systematic review;

• conduct a new systematic review within the Overview;

• use systematic reviews as a starting point to locate relevant studies with the intent of then extracting and analysing data from the primary studies (this would be considered a systematic review, or an update of a systematic review, and not an Overview);

• search for and include narrative reviews, textbook chapters, government reports, clinical practice guidelines, or any other summary reports that do not meet their pre-defined definition of a systematic review;

• extract and present just the conclusions of the included systematic reviews (instead, actual outcome data—narratively reported study-level data and/or meta-analysed data—should be extracted and analysed, and Overview authors are encouraged to interpret these outcome data themselves, in light of the Overview’s research questions and objectives);

• present detailed outcome data for primary studies not included in any included systematic review; or

• conduct network meta-analyses…”

“…the unit of searching, inclusion and data analysis is the systematic review rather than the primary study.”

“Although Overviews often present evidence from two or more systematic reviews of different interventions for the same condition or population, they should rarely be used to draw inferences about the comparative effectiveness of multiple interventions. This means that they should not directly compare interventions that have been examined in different systematic reviews with the intent of determining which intervention works ‘best’ or which intervention is ‘safest’.”

“We discourage indirect comparisons in Overviews. This is especially relevant for authors conducting Overviews that examine multiple interventions for the same condition or population; it is also relevant for authors regardless of whether the systematic reviews included in the Overview present their data using meta-analysis or simple narrative summaries of results. The reason is that the assumption underlying indirect comparison—the transitivity assumption—can rarely be assessed using only the information provided in the systematic reviews…”

“Overviews that examine multiple interventions for the same condition or population will often juxtapose data from different systematic reviews. Sometimes, these data appear in the same table or figure. Overviews that present data in this way can inadvertently encourage readers to make their own indirect comparisons. In cases where Overviews may facilitate inappropriate informal indirect comparisons, Overview authors must avoid ‘comparing’ across systematic reviews.”

“Overview authors should recognize that there will be some heterogeneity in the included systematic reviews and should consider whether or not the extent and nature of the heterogeneity precludes the utility of the Overview. Authors may find it helpful to consider whether:

• the systematic reviews are, or are likely to be, sufficiently up-to-date;

• the systematic reviews are, or are likely to be, sufficiently homogeneous in terms of their populations, interventions, comparators, and/or outcome measures (i.e., such that it would make sense from the end-user’s perspective that the individual systematic reviews were presented in a single product);

• the systematic reviews are, or are likely to be, sufficiently homogeneous in terms of what and how outcome data are presented (such that they provide a useful resource for healthcare decision making);

• the amount and type of outcome data presented is, or is likely to be, sufficient to inform the Overview’s research question and/or objectives; and

• the systematic reviews are, or are likely to be, of sufficiently low risk of bias or high methodological quality (i.e., authors should have reasonable confidence that results can be believed or that estimates of effect are near the true values for outcomes…”

None.

Cochrane Collaboration [6]

Update

Not reported.

Not reported.

Not reported.

“When deciding whether to update a particular review, the first consideration should be to determine whether the review question remains relevant to decision makers, and is well-targeted to answer current questions in policy and practice. Knowledge of the particular field will be required to answer this question. Checking whether the existing review is frequently accessed or cited can also be useful to indicate whether there is a need to update. A second aspect to this question is whether the original review was conducted well and used appropriate methods (Garner et al 2016). If the review question remains fundamentally of interest, additions and improvements may be possible to enhance the review’s methods (see Section IV.3.4). Depending on the changes required, it may be more appropriate to conduct a new review from scratch meeting current standards. A comparison between currently recommended methods and the methods used in the review can identify any important changes required.”

None.

Agency for Healthcare Research and Quality [28]

Integration of existing systematic reviews into new reviews

Not reported.

Not reported.

Not reported.

“Although it is important for systematic reviewers to consider all potentially relevant primary studies, it may not be necessary that all potentially relevant prior systematic reviews be considered. It is more important to assess and include prior reviews that are most relevant and of high quality than to attempt to include all reviews. Several factors can be considered in assessing relevance, including the date(s) of the search (currency), and review methods. Relevancy should be assessed using the PICOT (population, intervention, comparison, outcome, time) framework.”

None.

Agency for Healthcare Research and Quality [15]

Integration of existing systematic reviews into new reviews

“Some described that including existing reviews sometimes enables them to cover a wider range of questions and elements of questions (as denoted by PICOTS) when existing systematic reviews address important aspects of new review key questions.”

Not reported.

“When incorporating existing reviews into a new or updated review, EPC members most often described qualitative or narrative incorporation of the existing reviews, noting that quantitative combination of findings (without going back to all primary studies) is more difficult and potentially introduces error, and thus, is less commonly done.”

“Methods by which relevant existing systematic reviews can be evaluated for quality of methodological approach, using AMSTAR or other commonly used tools, with a focus on potentially incorporating only reviews meeting certain quality criteria into the proposed review…”

“there are other instances when it would not make sense to use an existing review, such as when there are few studies on a given topic or when there are multiple conflicting systematic reviews.”

“If more than one high-quality review is found with discordant findings, it may be an indication to start a de novo review on that key question.”

“Overall themes were identified from the discussions with EPCs:

• EPCs most commonly used existing reviews as a source of relevant literature and as context for the introduction or discussion section of reviews.

• Existing reviews were most useful when key questions and/or PICOTS-SD (population, intervention, comparator, outcome, time frame, setting, and study design) matched or when they addressed a specific subquestion of the new review.

• Using existing reviews was often more resource intensive than completing a review from scratch.

• EPCs expressed that they often did not trust aspects of reviews conducted by others.

• When relevant and rigorous, incorporating prior reviews into the review being undertaken by the EPC was clearly valuable in at least two instances: 1) allowing larger scope of the review being undertaken without additional resources, or 2) providing summarized evidence when a new in depth review of primary literature would not be feasible (for example, existing reviews provide individual patient data analysis or include hundreds of trials, supplemented by author-provided data).”

Belgian Health Care Knowledge Centre [29]

Meta-review/ review of reviews

Not reported.

Not reported.

Not reported.

“The main factors that have to be taken into account when deciding to perform a meta-review are the amount of reviews available on the topic and the time available for doing a review. In general a shortage in time and/or a high number of reviews available, may favour the decision to do a meta-review.”

“No general guidelines exist but from a pragmatic point of view it is advisable to discuss in the research team if a meta-review is a viable option, if there are approximately 5-10 or more recent reviews fairly matching your research question.”

“Other factors to consider in the decision:

• Applicability of published reviews to your topic: are the reviews really about the intervention you are interested in and did they extract data on the outcome of your interest?;

• Recency of the reviews, especially the search date is essential: it is good to take the search of one of the reviews and rerun it to see how many recent primary studies will be missing and to estimate if these could possibly alter the review conclusions;

• Methodological quality of reviews: are the reviews well performed? Hereto an assessment tool can be applied, e.g. AMSTAR85 as also proposed in the general KCE process notes (other assessment instruments exist and an overview is presented in among others Zeng et al. (2015) and Pieper et al. (2014);

• Number of included studies in reviews and overlap between the reviews: if most or all (recent) reviews only include one or two studies, it has probably not much sense to do a new review, but if each review includes tens of primary studies with only a small overlap, this pleas for a new review;

• Availability of meta-reviews: it can well be the case that on popular topics, one or more meta-reviews already exist, and if so the decision to do a new one should be weighted with the same factors as mentioned above. It can also be considered to do a review of meta-reviews, but in general this is not advised because the primary evidence is getting out of sight.

No clear-cut decision process can be presented here; it really needs discussion in the research team. There are many trade-offs in determining whether it is more efficient, and a methodologically sound process to rely on a prior review or to start from scratch. And keep in mind that a meta-review can only be as good as the reviews and primary studies on which it is based.”

“There are pros and cons for this approach. Main assumed advantage of doing a meta-review is time saving since someone else already searched, sifted, assessed and analysed the available evidence from primary studies. On the other hand reviews are on a higher abstraction level than primary studies and it may be difficult to get grasp on what really happened and how it was studied; details are lost. Moreover, when performing a meta-review, you are dependent on the intervention and outcome criteria that were formulated by others and these may be slightly different from what you want for your research question.”

World Health Organization [30]

Update

Not reported.

Not reported.

Not reported.

“It is not always necessary to commission a new systematic review (see Fig. 8.1). If one or more relevant, current and high-quality systematic reviews exist, these should be used. Updates, if needed, are usually less expensive and time-consuming than new reviews.”

“…updating an existing systematic review is a reasonable option provided a high quality, fully reported review exists that uses current methods for identifying, appraising and synthesizing the evidence.”

“To assess relevance, compare the key question of the existing systematic review to the key questions that were developed during the guideline scoping exercise, considering each component of PICO. Most frequently, the existing review does not entirely match the current key question. Nonetheless, the review may address one facet of WHO’s key question or provide useful background information, and the list of included studies may inform WHO’s systematic review.

If the existing systematic review addresses one of the key questions of the guideline, then its quality should be assessed. The following checklists may be used to assess the quality of systematic reviews:

• assessment of multiple systematic reviews (AMSTAR) (11), or R-AMSTAR (12);

• Oxman and Guyatt index for the quality of review articles (1991) (13).

“Once a systematic review has been found relevant and of high quality, whether it is up to date or not must be determined. There is no rule for dismissing a review on the basis of the time since publication (for example, two years); it depends on the topic and on the availability and rate of production of new information.”

Agency for Healthcare Research and Quality [18]

Replacing de novo processes using existing systematic reviews

Not reported.

Not reported.

Not reported.

“If the selected relevant, high-quality SRs have discordant findings, EPCs should explore the reasons for these disagreements. If EPCs cannot readily give reasons for the discordant findings, then they can regard this as an indication that they need to adopt a de novo approach to answer that key question.”

“If EPCs find that several recent, relevant, and high-quality SRs are appropriate for a given CER, they then need to determine how best to proceed. One approach is to incorporate the single “best” existing SR (most relevant and least biased) into their own reports [6]. However, selecting a single review may pose the risk of introducing selection bias; EPCs must ensure transparency in their criteria for eligibility. Another approach is to conduct a meta-review (also known as an “umbrella review”), whereby they select all relevant, high-quality SRs that meet an a priori publication date threshold and then assess the consistency among them [26, 27].”

“In general, good-quality SRs should be defined as those that have few or no methodological shortcomings and a low risk of bias. Fair-quality SRs have some methodological flaws but the EPC conducting the CER determined that the flaws will not seriously bias or invalidate the results. Poor-quality SRs contain a serious flaw or flaws that, in the judgment of the EPC conducting the CER, are highly likely to bias or invalidate the results.”

Agency for Healthcare Research and Quality [19]

Using existing systematic reviews

Not reported.

Not reported.

Not reported.

“…reviews should be excluded when the number of primary studies is small and any gains in efficiency by using the reviews would be minimal at best.”

“Systematic reviews should be as free of bias as possible if they are to reliably inform guideline recommendations or other policy decisions (2). Quality assessment of existing systematic reviews is therefore a critical step and should address both the methods used by the systematic reviewers to minimize bias as well as the transparency and completeness of reporting of review methods, individual study details, and results. In fact, the priority should be to include existing systematic reviews adhering to high methodological standards, rather than to routinely include all existing systematic reviews in order to be comprehensive.”

“…when higher-quality reviews disagree, a new independent review that carefully addresses potential sources of disagreement with careful sensitivity or subgroup analyses may be the most informative strategy.”

Recommendations from 8 HTA agencies* [31]

*The 8 HTA agencies were the Agency for Quality and Accreditation in Health Care (AAZ, Croatia), Centre for Reviews and Dissemination (CRD, UK), Gesundheit Österreich GmbH (GÖEG/BIQG, Austria), Health Care Improvement Scotland (HIS, UK), Institute for Quality and Efficiency in Health Care (IQWiG, Germany), Belgian Federal Health Care Knowledge Centre (KCE, Belgium), Ludwig Boltzmann Institute for Health Technology Assessment (LBI-HTA, Austria), and National Institute for Clinical Excellence (NICE, UK).

Overview

Not reported.

Not reported.

Seven of the HTA agencies were open to searching for primary studies.

“According to two HTA agencies, a narrative synthesis instead of a quantitative synthesis should be performed, while the third agency only notes that an evidence synthesis is likely to be problematic.”

“In the context of overviews, a meta-analysis of meta-analyses should turn out to be difficult as some of the primary studies will usually be included in more than one meta-analysis. Pooling results would give too much statistical power to multiple included primary studies (Smith et al., 2011). Other ways of presenting findings will have to maintain a reasonable balance between complexity and a potential loss of important findings from the reviews.”

“Five of the HTA agencies have prerequisites for the conduct of overviews (Table 1). All of them state that relevant SRs must be of high quality, although only one HTA agency concretizes this by setting cut-off points for the review quality, based on the assessment with a critical appraisal tool.”

“Overviews should be updated when the corresponding reviews have been updated.”

Centre for Reviews and Dissemination at the University of York [3]

Update

Not reported.

Not reported.

Not reported.

“If an existing review is identified which addresses the question of interest, then the review should be assessed to determine whether it is of sufficient quality to guide policy and practice. In general, a good review should focus on a well-defined question and use appropriate methods. A comprehensive search should have been carried out, clear and appropriate criteria used to select or reject studies, and the process of assessing study quality, extracting and synthesizing data should have been unbiased, reproducible and transparent. If these processes are not well-documented, confidence in results and inferences is weakened. The review should report the results of all included studies clearly, highlighting any similarities or differences between studies, and exploring the reasons for any variations.”

“If a high quality review is located, but was completed some time ago, then an update of the review may be justified. Current relevance will need to be assessed and is particularly important in fields where the research is rapidly evolving. Where appropriate, collaboration with the original research team may assist in the update process by providing access to the data they used. However, little research has been conducted on when and how to update systematic reviews and the feasibility and efficiency of the identified approaches is uncertain [11]. If a review is of adequate quality and still relevant, there may be no need to undertake another systematic review.”

None.

Review of reviews

“Reviews of reviews are likely to be helpful when a review question is very broad and a number of systematic reviews have already been conducted in the topic area.”

Not reported.

Not reported.

“Reviews of reviews are likely to be helpful when a review question is very broad and a number of systematic reviews have already been conducted in the topic area.”

None.

Tugwell et al. [17]

Replication, defined as:

• “Direct replication by purposeful repetition to verify the findings of the original research question; or

• Conceptual replication by purposeful broadening or narrowing of the research question in existing systematic reviews (e.g., across broader or more focused populations, intervention types, settings, outcomes, or study designs)”

Not reported.

“The need for replication of systematic reviews arises from concerns or lack of clarity about the technical or statistical methods or the judgments made, such as the subjective decisions related to defining criteria for inclusion of the population, intervention or exposure, and outcomes of interest; and data collection, synthesis, and interpretation [8].”

Not reported.

“Question 2. Is it likely that direct replication by repetition or conceptual replication by broadening or narrowing of the scope will address uncertainties, controversies, or the need for additional evidence related to:

2.1. The framing of the question in previous reviews?

2.2. The conduct and reporting of previous reviews?

2.3. Author influence or conflicts of interest in previous reviews?

2.4. Discordant findings in previous reviews?”

The authors included a replication comparative worksheet for appraising the body of evidence that can include multiple systematic reviews.

Noble et al. [2]

Systematic review

“…to address a highly focused clinical question.”

Not reported.

“Evaluates and summarizes the findings of all relevant individual studies, and if appropriate, combines the results of several studies to provide more reliable results.”

Not reported.

“The ‘gold standard’ of reviews because the review is based on explicit, prespecified and reproducible methods used to systematically search all sources of evidence and critically appraise, summarize and synthesize research findings…”

Review of reviews/ umbrella review

“Useful when a review question is very broad and a number of systematic reviews have already been conducted in the topic area.”

Not reported.

“Compiles evidence from multiple research syntheses in order to summarize existing evidence and like systematic reviews follow clear methods.”

“Useful when a review question is very broad and a number of systematic reviews have already been conducted in the topic area.”

“…the different inclusion criteria adopted by the reviews included can make interpretation problematic.”

Ballard et al. [32]

Overview

“Overviews facilitate these broad comparisons…”

“Overviews examine: (1) different interventions for the same condition or population (e.g. Jones et al., 2012), (2) the same intervention for different conditions or populations (e.g. Steultjens et al., 2005), (3) multiple outcomes of the same intervention for the same condition or population (e.g. Flodgren et al., 2011), or (4) adverse effects from the same intervention across multiple conditions (e.g. Singh Jasvinder et al., 2011).”

“…they serve the following three functions:

1. To identify gaps in the literature where multiple comparable studies may exist but a research synthesis has not been performed (Caird et al., 2015; Piso et al., 2015; Ryan et al., 2009; Cooper and Koenka, 2012; Santaguida et al., 2013)

2. To compare and contrast existing systematic reviews (Aromataris et al., 2014; Aromataris et al., 2015; Baker et al., 2014; Conn and Coon Sells, 2014; Cooper and Koenka, 2012; Pieper et al., 2014a; Pieper et al., 2012; Santaguida et al., 2013; Smith et al., 2011).

3. To provide a summary of evidence from existing systematic reviews, with or without synthesis (Becker and Oxman, 2011; Caird et al., 2015; Cochrane Comparing Multiple Interventions Methods Group, 2012; Cochrane Comparing Multiple Interventions Methods Group, 2013; Cooper and Koenka, 2012; Hartling et al., 2012; Hartling et al., 2014; Li et al., 2012; Pieper et al., 2014a; Pieper et al., 2012; Piso et al., 2015; Ryan et al., 2009; Smith et al., 2011; Thomson et al., 2013; Thomson et al., 2010).”

Not reported.

“As Pieper et al. (2012) point out, it is important to differentiate between methodological quality, which considers how well the systematic review was conducted, and reporting quality, which considers how well systematic reviewers have reported their methodology and findings. For this reason, it has been recommended that PRISMA be used in conjunction with a comprehensive, validated critical appraisal tool (Pieper et al., 2012; Shea et al., 2007; Oxman and Guyatt, 1991).”

None.

Lunny et al. [33]

Overview

“Overviews are typically broader in scope than systematic reviews (SRs) and may examine different interventions for the same condition, the same intervention for different conditions, or the same intervention for the same condition but focusing on different outcomes [5,6,7,8].”

“2.1 Define the purpose of the overview

2.1.1 Map the type and quantity of available evidence (e.g. types of interventions, outcomes, populations/settings, study designs but not effects)

2.1.2 Compare multiple interventions with the intent of drawing inferences about the comparative effectiveness of the interventions intervention for the same condition, problem or population

2.1.3 Summarize the effects of an intervention for the same condition, problem or population where different outcomes are addressed in different SRs

2.1.4 Summarize the effects of an intervention across conditions, problems or populations (e.g. “borrowing strength” when there is sparse data for a single condition and a similar mechanism of action for the intervention is predicted across conditions)

2.1.5 Summarize unexpected (including adverse) effects of an intervention across conditions, problems or populations

2.1.6 Identify and explore reasons for heterogeneity in the effects of an intervention (e.g. by examining reasons for discordant results or conclusions across SRs)”

Not reported.

Not reported.

None.

Garner et al. [8]

Update of a systematic review

“An update asks a similar question with regard to the participants, intervention, comparisons, and outcomes (PICO) and has similar objectives; thus it has similar inclusion criteria.”

Not reported.

Not reported.

Not reported.

“Decisions about whether and when to update a systematic review are judgments made at a point in time. They depend on the currency of the question asked, the need for updating to maintain credibility, the availability of new evidence, and whether new research or new methods will affect the findings.”

Hartling et al. [34]

Systematic review

“A limitation of SRs, as they have evolved within the healthcare field, is that often they are narrow in scope and may exclude competing interventions for a given condition. They often focus on direct pairwise comparisons and may lack formal comparisons across different interventions that are critical for informed decision making by end-users, including clinicians, policymakers and consumers.”

Not reported.

Not reported.

“The purpose of SRs is to collate relevant evidence from individual studies to answer a specific research question.”

None.

Overview

“Overviews compile information from multiple SRs in order to provide a comprehensive synthesis of the evidence examining: different interventions for the same condition; different outcomes for the same intervention in the same condition; the same intervention for different conditions or populations; or adverse effects from the same intervention across multiple conditions (27).”

Not reported.

“The Cochrane Multiple Intervention Methods Group now emphasizes that overviews should not simply summarize SRs, rather they should integrate or synthesize the

evidence (36).”

“…conducting an NMA may be challenging within the context of an overview, given the previously mentioned inconsistencies among individual SRs.”

“Overviews compile data from multiple SRs…”

“Because an overview is based on existing SRs that have already identified the relevant studies and extracted data, carrying out an overview is more feasible and efficient than undertaking an SR.”

“…the authors are dependent on the decisions and methods used within the relevant SRs.”

Comparative effectiveness review

“In this article, we use the term ‘comparative effectiveness review (CER)’ to refer to a review that collates evidence from individual studies to describe the relative benefits (or harms) of a range of interventions. These reviews use explicit, systematic methods similar to those of SRs. They may be considered SRs; however, they are generally broader in scope than the focused pairwise comparisons typical of Cochrane SRs, the reason for distinguishing them in this article. Furthermore, they may be broader in terms of including both randomized and nonrandomized studies in order to identify measures of effectiveness and safety. They differ from overviews in that, for the most part, they focus on primary studies rather than SRs as the unit of analysis.”

Not reported.

Not reported.

Not reported.

None.

Cooper et al. [35]

Overview

“…overviews often seek to answer questions that are much broader in scope than questions that are typically asked by a single research synthesis.”

Not reported.

Not reported.

Not reported.

“If an overview is meant to replace the syntheses it covers, then it is even further removed from the research front.”

“…overviewers would be well served to include a section in their report in which they at least reference and discuss what these recent advances are and how they relate to the work covered in the constituent research syntheses (see also Thomson et al., 2010).”

Grant et al. [10]

Umbrella review

“Each umbrella review focuses on a broad condition or problem for which there are two or more potential interventions and highlights reviews that address these potential interventions and their results.”

“…a response, and potential solution, to the perennial dilemma reviewers face regarding ‘lumping’ versus ‘splitting’, i.e., whether the needs of a particular field or area are best addressed by a broad review that covers multiple interventions at the cost of lost detail and specificity or by a succession of focused reviews that address specific comparisons at the risk of fragmenting the overall picture.”

“…compiling evidence from multiple reviews into one accessible and usable document.”

“Graphical and tabular with narrative commentary”

“Identification of component reviews, but no search for primary studies”

None.