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What Do You Do When Potential for Study Population Overlap in Reviews

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Managing overlap of primary written report results across systematic reviews: practical considerations for authors of overviews of reviews

BMC Medical Research Methodology book 21, Commodity number:140 (2021) Cite this article

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Abstract

Background

Overviews frequently identify and synthesise a large number of systematic reviews on the aforementioned topic, which is probable to lead to overlap (i.e. duplication) in primary studies across the reviews. Using a master report result multiple times in the same analysis overstates its sample size and number of events, falsely leading to greater precision in the analysis. This paper aims to: (a) describe types of overlapping information that arise from the same primary studies reported across multiple reviews, (b) describe methods to identify and explain overlap of primary written report data, and (c) present six example studies illustrating unlike approaches to manage overlap.

Methods

We first updated the search in PubMed for methods from the MOoR framework relating to overlap of principal studies. One author screened the studies titles and abstracts, and whatever full-text articles retrieved, extracted methods data relating to overlap of principal studies and mapped it to the overlap methods from the MOoR framework. Nosotros besides describe six case studies as examples of overviews that employ specific overlap methods beyond the steps in the conduct of an overview. For each example study, we hash out potential methodological implications in terms of limitations, efficiency, usability, and resource use.

Results

9 methods studies were found and mapped to the methods identified by the MOoR framework to address overlap. Overlap methods were mapped across four steps in the acquit of an overview – the eligibility criteria step, the data extraction footstep, the assessment of chance of bias step, and the synthesis stride. Our overview case studies used multiple methods to reduce overlap at unlike steps in the behave of an overview.

Conclusions

Our study underlines that there is currently no standard methodological approach to bargain with overlap in primary studies across reviews. The level of complexity when dealing with overlap can vary depending on the yield, trends and patterns of the included literature and the telescopic of the overview question. Choosing a method might exist dependent on the number of included reviews and their primary studies. Gaps in evaluation of methods to address overlap were constitute and farther investigation in this surface area is needed.

Peer Review reports

Groundwork

Navigating the expanding trunk of enquiry literature is an increasing challenge for health practitioners, researchers and decision-makers. Global research output as a whole is growing rapidly, and it is estimated that every 9 years, publications in Web of Science double [1]. The number of published systematic reviews existence produced yearly is also expanding [ii, 3], and duplication of reviews on like topics is common. For example, Doundoulakis et al. [iv] found 57 meta-analyses on direct oral anticoagulants for stroke prevention in atrial fibrillation. Their inclusion criteria were meta-analyses with comprehensive search strategies and risk of bias assessments. If their eligibility criteria had been less restrictive, over 100 meta-analyses would have been constitute on this topic. Faced with a big book of systematic reviews on the same topic, healthcare providers demand a method to make sense of potentially conflicting, discrepant and overlapping information of varying quality [iii].

Overviews of systematic reviews (i.eastward. umbrella reviews, meta-reviews, reviews of reviews, or reviews of meta-analyses [henceforth called overviews] [5]), offer a solution to this challenge by proposing a method to synthesize the results and conclusions at the systematic review level [half dozen, 7]. Overviews are increasing in volume in response to the growing number of systematic reviews. From 2000 to 2020, 1218 overviews were published, the majority of which (886/1218 [73%]) were published in the about recent 5 year menstruum (2016-2020) [eight].

Overviews oftentimes identify and synthesise a large number of systematic reviews on the same topic, which is probable to lead to overlap (i.e. duplication) in primary studies across the reviews. For example, a broad overview of 16 natural therapies, found largely to exist ineffective, led to changing Australia'southward Private Health Insurance Act of 2007 [9]. Overlap tin can arise when systematic reviews on the same topic include one or more than identical primary studies (e.g. randomised control trials (RCTs), cohort and cross-sectional studies). The overlapping data from the same primary studies reported across multiple systematic reviews may include: overlapping gamble of bias assessments, overlapping pooled issue estimates across similar outcomes, overlapping meta-analysis results (e.grand. Iii heterogeneity statistics), or overlapping certainty of the evidence assessments (due east.g. Grading of Recommendations, Assessment, Development and Evaluations (GRADE)) [half-dozen, 7].

Case of overlapping primary report data

Synthesising systematic reviews with overlapping primary written report data is a claiming for overview authors. As an example, we present iii reviews included in a fictional overview, each with a gear up of RCTs, which are indicated by the coloured boxes in Fig. 1. One of the potential options for dealing with the overlap in RCTs is to base of operations the results on only i systematic review using methodological criteria to select that review, for case, choose the review with the greatest number of trials (i.e. Review 1 with viii trials). However, this 2008 review is out of date, and leaves out the 4 more recent trials. Alternatively, overview authors could cull Review 2 with the highest quality. Yet, this high quality review omits 6 trials. A tertiary option is to include the most recent review, Review 3, only again 6 trials would be omitted.

Fig. one
figure 1

Three reviews included in a fictional overview with overlapping randomised control trials (RCTs)

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Alternatively, all the reviews could be included, which then involves quantifying the overlap and considering its influence when summarizing the results across the reviews (narratively or statistically). The methods used to deal with overlap of trials equally highlighted hither, could influence the interpretation of results and conclusions of the overview.

Overlap is a problem of precision related to sampling (i.eastward. information technology is non a bias). The inclusion of the same master study in more than i systematic review gives undue weight to this report. Using a study multiple times in the same analysis overstates its sample size and number of events, falsely leading to greater precision in the assay. This may affect both narrative description of the results, or a statistical synthesis (eastward.g. including the results from a chief study more than once in the aforementioned meta-analysis).

Methods development

Mapping, evaluation and evolution of methods used in overviews has grown over the last 12 years [10,11,12,13,14,15,xvi]. A systematic map of all methods used in overviews, called the MOoR framework, identified nine methods to manage the overlap used across four steps in the conduct of an overview [7, xvi]. Since publication of the MOoR framework, methods for overlap take been published [17,eighteen,19]. These methods are currently existence used in practice, and overview guidance has been recently updated [19, 20], simply there has been limited evaluation of these methods.

This newspaper aims to: (a) describe the different types of overlapping data that arise from the same primary studies reported across multiple reviews, (b) depict methods to identify and explicate overlap of primary study data, and (c) nowadays half dozen example studies illustrating dissimilar approaches to manage overlap.

Methods

Nosotros first updated the search for methods from the MOoR framework [7, xvi, 21] relating to overlap of master studies. Nosotros conducted a search in PubMed using the following algorithm: (method*[TI] OR meta-epidemiol*) in combination with the Boolean operator AND, and the search filter for overviews developed past Lunny et al. [5] (Boosted file ane: Appendix A). Nosotros also conducted forward commendation searching on a fundamental study from 2014 [13] dealing with overlap using Google Scholar. Search dates were from January 2016 to March 2020.

We considered articles eligible for inclusion if they described methods used to manage overlapping data beyond primary studies in overviews of wellness interventions.

Inclusion criteria:

  1. a.

    Articles describing methods for overviews of systematic reviews of wellness interventions

  2. b.

    Articles examining methods used in a cantankerous-section or cohort of overviews

  3. c.

    Guidance (e.yard. handbooks and guidelines) for undertaking overviews

  4. d.

    Commentaries or editorials that hash out methods for overviews

Exclusion criteria:

  1. a.

    Articles published in languages other than English

  2. b.

    Articles describing methods for network meta-analysis

  3. c.

    Protocols or registered reports

  4. d.

    Articles exclusively virtually methods for overviews of other review types (i.e. not of interventions)

Ane author screened the studies titles and abstracts, and whatsoever full-text articles retrieved, against the inclusion criteria. 1 author extracted methods data relating to overlap of chief studies and mapped it to the overlap methods from the MOoR framework (Boosted file 1: Appendix B). Characteristics of studies were extracted by one reviewer, as well as the characteristics of the case studies. Results are presented descriptively and in tables.

We also depict six instance studies [22,23,24,25,26,27] equally examples of overviews that employ specific methods across the steps in the conduct of an overview. The case studies were selectively chosen based on the variety of different approaches used to manage overlap. For each case study, nosotros will discuss potential implications in terms of methodological limitations, efficiency, usability, and resources use.

Results

Screening results

Our search strategy retrieved 119 unique records, and the frontwards commendation searching retrieved 92 citations (Fig. two). Later on deduplication 199 remained, and later on screening abstracts and total text, seven were included [17,18,19, 28,29,30,31]. I boosted conference commendation was found through good knowledge on the topic [32], and one paper recently published was included after completion of the first typhoon [33].

Fig. 2
figure 2

Flowchart of included studies

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Characteristics of methods studies

Six studies were manufactures describing methods for overviews, ii were guidance documents, and i was an empirical study (Table one).

Tabular array 1 Characteristics of methods studies on overlapping principal study data across reviews

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Methods studies identified and mapped to the MOoR framework

9 studies were mapped to the methods identified by the MOoR framework to address overlap (Table two). Several methods map across four steps in the acquit of an overview – the eligibility criteria step, the information extraction footstep, the assessment of risk of bias step, and the synthesis step. Seven of the nine studies looked at methods at the eligibility criteria step. One of these studies empirically evaluated the impact of five inclusion decisions on the conduct of an overview [19]. The authors found that when overviews contain overlapping principal studies, selecting a Cochrane systematic review, equally opposed to the about contempo or highest quality non-Cochrane review, maximized the amount of effect data included in the overview [19].

Tabular array 2 Methods identified from the MOoR Framework mapped to newly identified studies

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At the eligibility criteria footstep, one common strategy is to limit the number of included reviews in the overview. This method can be addressed past selecting 1, or a subset of systematic reviews from multiple addressing the same question using pre-specified quality criteria (e.g. select systematic reviews that are of high quality) or take a particular methodological approach (due east.g. select systematic reviews with meta-assay of iv or more principal studies) (Table 2).

To determine if overlap is present, methods proposed in the data extraction pace can allow abstraction of data required for cess of the extent of the overlap across systematic reviews. Overlapping data from primary studies can so be managed using multiple methods at the synthesis step, including the options to: (a) use decision rules to select results for assay from i, or a subset of systematic reviews, (b) determine methods for quantifying overlap, or (c) use statistical approaches to deal with overlap. Many methods such as quantifying overlap using the corrected covered area (CCA [13]), or visually examining and presenting overlap of the main studies across systematic reviews may not directly address the event just may provide data on the nature and extent of the problem.

Overlap in data tin also ascend from duplicate risk of bias/quality assessments, or duplicate Grade outcome assessments. Run a risk of bias data from the same principal study tin differ between what is reported in systematic reviews due to:

  • mistake in data extraction [34]

  • data extracted from dissimilar sources for the same primary written report (eastward.yard. different reports, unpublished data) [35]

  • data retrieved/not retrieved by contacting master report authors [36]

  • dissimilar tools used to appraise risk of bias which leads to missing or inconsistent data about potential biases [37], and/or

  • conflicting information reported to support judgements for the aforementioned chance of bias tool [38].

Discrepant and overlapping risk of bias assessments across systematic reviews can be resolved by: (a) extracting the run a risk of bias assessment of primary studies from the included systematic reviews, using data extraction approaches to manage missing, flawed assessments, or discrepant assessments of the same main study; or (b) re-assessing all master studies using a common risk of bias tool. The data extraction approaches outlined in the MOoR framework to manage discrepant data across systematic reviews involve retrieving either published or registry reports of the primary studies, or contacting systematic review or primary written report authors, or both, for clarification regarding discrepancies [7, sixteen].

Authors tin can have boosted steps to manage overlapping information and data at the synthesis stage [7, sixteen]. Two non-statistical methods for resolving overlap in primary studies were identified in the MOoR framework:

  • Select the result of one (or a subset of) systematic reviews with or without meta-assay using a decision rule or a published algorithm [39,twoscore,41]

  • Place systematic reviews with or without meta-analysis with 25% or more of their research in common and eliminate the one with the fewer studies [11]

Three statistical methods for addressing the overlap in primary study information across systematic reviews were identified in the MOoR framework:

  • Conduct sensitivity analyses (e.g. second-order meta-analysis (MA) including all MAs irrespective of overlap compared with second-lodge MA including only MAs where there is no overlap in master studies) [11]

  • Inflate the variance of the MA judge [42]; that is, an inflation gene of J tin exist multiplied with the 2nd order MA variance to correct for the underestimated variance reckoner.

Presentation of case studies

Choosing between overlap methods often depends on the blazon of review existence conducted and the clinical topic being investigated. To illustrate how authors used these methods, we now present six case studies to illustrate examples of methods used at dissimilar steps in the carry of an overview, with a commentary on potential implications of the methods in terms of methodological limitations, efficiency, usability, and resource use.

i) Bidonde et al. exercise for adults with fibromyalgia

The overview by Bidonde [22] evaluates physical activity interventions for adults with fibromyalgia with a focus on four outcomes: hurting, multidimensional function, concrete function and adverse effects. To restrict the number of included reviews, the authors get-go selected simply reviews meeting three or more of Cochrane's criteria of a systematic review. These were: (a) a focused question (i.e., contains PICO [population, intervention, comparison, outcome] statement); (b) a comprehensive and explicit search (i.e., more than i database and other sources searched, keywords or Mesh terms given); (c) the use of explicit criteria to include and exclude RCTs; (d) explicit methods of extracting and synthesising study findings (quantitative); and (e) inferences made were evidence based.

The authors chose to deal with overlap at the synthesis, presentation and summary of findings footstep using quantification of the amount of overlap and presenting the results (Table two). The authors counted 29 (48%) RCTs overlapping across 9 reviews, 31 (52%) of which were 'unique' RCTs, and presented the information in tables. For each review, the number of included RCTs was reported, followed past the number of overlapping RCTs betwixt the review and any other reviews. Here is an exemplary quote illustrating this: "[The overview by] Kelley 2010 included vii RCTs: three overlapped with [the overview by] Bidonde, six with [the overview by] Hauser, 3 with [the overview by] Lima, one with McVeigh, and two with Ramel".

The methods described here to deal with overlapping principal studies are resource-friendly. The method to restrict inclusion to systematic reviews aid reduce the corporeality of overlap and during the synthesis phase, overlap is quantified. Neither of these methods resolve the problem of overlap, in the same way that judging studies at low or high quality does not resolve the issue of the inclusion of depression quality testify in a review. As with quality appraisal, overlap should be minimised, quantified and used to contextualise the results and conclusions of the overview. Ordering results by amount of overlap may increase the prominence of studies with low overlap, focusing attention on the results that should most influence conclusions. Synthesis of the results of reviews tin be express to those with footling or no overlap equally a sensitivity analysis.

2) Patnode et al. tobacco cessation in adults

We present the example of an overview by Patnode and colleagues [27], which aimed to compare and synthesise systematic review-level evidence of the effectiveness and safety of pharmacotherapy and behavioral tobacco cessation interventions among adults, including pregnant women and those with mental health weather condition. Patnode [27] used 9 methods to bargain with the overlap in master studies across 54 included systematic reviews beyond 4 steps in the carry of an overview (Table 2). To manage the overlap in master studies, the authors chose to exclude non-systematic reviews. At the data extraction and the assessment of hazard of bias steps, they chose to exclude all low quality systematic reviews. Quality of the reviews was assessed using the AMSTAR tool [43]. These methods restrict the number of systematic reviews that the authors must analyse at the synthesis pace.

At the synthesis step, the authors developed a conclusion rule. If multiple expert quality systematic reviews were identified, the decision rule was applied to decide which systematic review represented the most comprehensive, upward-to-date literature base of operations and highest quality to serve every bit the basis for the main findings (called "primary reviews"). To examine and quantify the amount of overlap across the included reviews at the synthesis step, included primary studies inside each systematic review were compared to evaluate the comprehensiveness of each review and duplication in the included primary literature. Finally, overlap was visually presented in tables and figures.

The findings of the Pollock study [19] suggest that eliminating systematic reviews may lead to loss of information. Yet, without specific empirical testing, it is non known whether the Patnode [27] overview suffered from a loss of information from eliminating depression quality reviews. If Patnode [27] had included all systematic reviews and so older, less comprehensive, and low-quality systematic reviews would have been included, thus introducing untrustworthy evidence into the results of the overview. By limiting their findings to loftier quality and comprehensive systematic reviews, Patnode and colleagues [27] gain efficiency in the overview production, reduce human resources needed to synthesise a large number of overviews, and produce an overview that is potentially more readable and useable.

iii) Murphy et al. cocky-management interventions in chronic obstructive pulmonary disease

Nosotros describe the overview by Irish potato [23] that aimed to determine the clinical effectiveness of self-direction interventions for adults with chronic obstructive pulmonary affliction (COPD). Cocky-direction interventions were defined as "structured and personalized, and often multi-component, with goals of motivating, engaging and supporting the patients to positively suit their health behaviors and develop skills to better manage their disease" [44]. Murphy et al. used v methods, across the iv steps in the conduct of an overview, to manage the overlap in 165 unique chief studies across the sixteen included systematic reviews (Table 2). To manage overlap of primary studies, called "crossover" past the authors, they first included all studies based on pre-determined eligibility criteria. During data extraction and assessment of risk of bias stage, overlap across systematic reviews was assessed (Table 2). In the case of substantial overlap (over 70%), the higher quality review (using R-AMSTAR [45]) was selected if information technology was published the aforementioned year or more than recently than the comparison reviews.

Overlap of primary studies was visually presented in tables. Overlap was calculated as the proportion of primary studies from ane systematic review found in some other, nevertheless this was not explicitly stated in the methods. In not explicitly reporting how overlap, or crossover, was calculated, reproducibility is jeopardized. Furthermore, the authors practise not report the reference review for calculation of per centum overlap. Without noesis of the reference review, percentage overlap is not reproducible [46]. Finally, the tabular array reporting the overlap of RCTs across reviews has no legend to guide the reader in its estimation. Given the multiple methods for managing overlap, authors of overview should explicitly and entirely state methods used in calculation and cess of overlap.

Murphy et al. excluded two systematic reviews for high overlap (Bentsen and Harrison). The college quality (and thus included) reviews (Zwerink and Jordan) included significantly more principal studies.

In both cases, systematic reviews with a low number of primary studies (Bentsen et Harrison) were excluded in favour of systematic reviews with significantly more master studies (Zwerink et Jordan). During data synthesis, the authors noted that meta-analysis at the overview level would be inappropriate given the high per centum of overall overlap constitute.

In summary, the management of overlap focused on the information extraction, assessment of gamble of bias and synthesis stages whilst maintaining broad eligibility criteria. Transparent reporting of methods dealing with overlap are necessary to interpret and reproduce results of overlap in overviews [46]. In selecting the highest quality review with under 70% overlap, Murphy et al. minimize the impact of duplicate primary studies in their overview. Past limiting the inclusion to current, high quality reviews, Tater and colleagues take a chance loss of information (Pollock [19]), but gain in utility, efficiency, and requiring potentially less resources.

4) Prousali et al. efficacy and safety of interventions to control myopia progression in children

This case written report involves an overview evaluating interventions aimed at slowing the progression of myopia in children [24]. Prevention of blindness and visual impairment from myopia was prioritised by the Earth Health Organisation (WHO)'s VISION 2020 campaign [47]. This overview identified 18 systematic reviews that synthesized the efficacy of a multifariousness of interventions for myopia from 44 unique primary studies (1989–2016). Prousali et al. used 5 methods across the iv steps in the comport of an overview to address overlap (Table 2). Eligible reviews had to meet pre-divers eligibility criteria for inclusion, which included systematic reviews of primary studies enrolling children or adolescents ≤18 years of age with myopia. Reviews without systematic search strategies or risk of bias assessment of primary studies were excluded. Interventions had to be optical or pharmacological and compared to single vision glasses, contact lenses or placebo. Chief outcomes were myopia progression and axial elongation.

A citation matrix was presented that identified principal studies that were included in more than than one review. Overlap was quantified at the review level (equally opposed to the result level) using the CCA [13] and loftier overlap was divers as equal to or more than 10%. If a review contained high overlap, reviews were retained that were (1) the most contempo, (2) contained the highest amount of information (not defined by the authors), and (3) had the lowest risk of bias using ROBIS [48] and GRADE [49]. A meta-assay was conducted using the unique principal studies included in the reviews. Overlap was considered moderate in this overview and was estimated at 6.2% using the CCA method. Since overlap was estimated at below ten%, all included reviews were retained in the assay.

The authors used the CCA to appraise overlap and country that it was "moderate" without explaining how moderate overlap may touch the overview's findings. The authors then go on to perform a new meta-analysis, thus ignoring their overlap assay, and removing the claiming of overlap from the equation. While conducting a 'de novo' meta-analysis eliminates the problem of very high or very low overlap, information technology is more resource intensive, may not always be feasible, and may innovate indirectness (i.e. lack of applicability) as the main studies were not screened confronting the overview's main objective and PICO eligibility criteria [l]. When there are pregnant differences between the PICO of the overview and the PICO of the primary studies included in the systematic reviews, certainty in the evidence decreases. A better strategy would have been to conduct a systematic review with the aim to include primary studies directed related to the Prousali'south research question, thus eliminating any trouble of indirectness.

5) Ryan et al. interventions to better safe and constructive medicines use by consumers

In this updated Cochrane overview of interventions to amend safe and effective medicines use by consumers [25], the authors searched the Cochrane database of systematic reviews (CDSR) and the Database of Abstracts of Reviews of Effects (Dare [51];). DARE contains summaries of methods and conclusions of included systematic reviews including a quality assessment. The authors deal with overlap at the eligibility criteria step using two methods, and i method at the cess of take chances of bias step (Table 2). Although it is common for Cochrane overviews to include simply Cochrane reviews, Ryan et al. did not impose this restriction. All Cochrane reviews meeting the overviews inclusions criteria were included, and non-Cochrane reviews were excluded if they had substantial duplication of content with Cochrane reviews and were of low quality. Non-Cochrane reviews were included that were non within the PICO telescopic covered by Cochrane reviews. The rationale for prioritising inclusion of Cochrane reviews over not-Cochrane reviews was that Cochrane reviews are regularly updated and are of higher quality [52,53,54,55].

Quality of the included systematic reviews was rated using two scales; the Heart for Reviews and Dissemination assessment every bit part of the Cartel, and the author'south assessment as judged using AMSTAR [43]. If reviews were classified equally low quality with Dare or AMSTAR (≤4 out of eleven possible points), they were excluded. Further, non-Cochrane reviews with more than a half of their studies already included in a Cochrane review were excluded. At the synthesis stage, Ryan et al. retained 1 Cochrane review with unique content thus eliminating any bug related to overlapping principal study information (i.due east. analysis of one high quality and comprehensive systematic review using conclusion rules (Tabular array 2)).

At that place are two major advantages to including but relevant Cochrane reviews in an overview. Kickoff, quality, recency and comprehensiveness is higher in Cochrane reviews when compared to not-Cochrane reviews [52,53,54,55]. Second, according to the Cochrane policy, two reviews cannot exist published on the same topic, resulting in a decreased gamble of overlapping chief studies across reviews. 3rd, an empirical study institute that selecting a Cochrane systematic review, equally opposed to the most contempo or highest quality not-Cochrane systematic review, maximized the corporeality of consequence data included in an overview [19], making that overview more relevant and useful for determination makers. However, including only Cochrane reviews of RCTs may limit data from highly relevant qualitative or quantitative reviews of observational studies.

6) Thabet et al. clinical and pharmacokinetic/dynamic outcomes of prolonged infusions of beta-lactam antimicrobials

Thabet et al. conducted an overview investigating the comparative efficacy of prolonged infusions beta-lactam antibiotics compared to traditional intermittent infusions in hospitalized patients with infection. The authors used four methods beyond three steps in the conduct of an overview to accost overlap (Tabular array 2). At the eligibility footstep, eligible systematic reviews must have systematically searched the literature and synthesised clinical outcomes that included mortality or clinical cure. At the data extraction step, all included systematic reviews were information extracted. Quantification and cess of overlap occurred at the synthesis step using citation matrices and by calculating the CCA at the outcome level beyond all included reviews and between each pairs of reviews.

Twenty-i reviews involving 71 master studies were included. For each of 9 clinical outcomes, a matrix of primary studies was created. Unique and overlapping studies were colour coded and overlap that was impossible due to publishing dates (i.e., primary study published after the systematic review) were also identified. Overlap was quantified using the CCA calculation across reviews for each outcome. Overlap thresholds, every bit determined by Pieper et al. [xiii], were used for interpretation of measured overlap (0–5% - slight, 6–10% - moderate, xi–15% - high, > 15% - very high). To further characterize overlap by outcome, CCA calculations for pairs of reviews were performed and presented as a grid (Fig. 3). Thabet et al. found that overlap was moderate to high for each outcome and percentage of unique references ranged from 38 to 78%. The authors suggest that the pairwise CCA filigree (Fig. 3) allows the reader to identify which combinations of paired reviews had the highest overlap, while the citation matrix (Fig. 4) allows the reader to run across which primary studies were common among reviews. The commendation matrix also helped the authors empathize why some studies were non identified by multiple reviews.

Fig. 3
figure 3

CCA calculations for pairs of reviews. Overlap categorization: 0–5% - slight (white), 6–x% - moderate (light-green), eleven–15% - high (yellow), > fifteen% - very high (red)

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Fig. four
figure 4

Citation matrix. Green indicates a trial included in a review, scarlet indicates a trial excluded or omitted from a review and black indicates that the dates of publication make a trial ineligible for inclusion in a review

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In this overview, the authors explain how both high overlap and low overlap influenced the findings of the overview. By including all the systematic reviews identified past the search, data mapping exercises identified significant variability between reviews with respect to telescopic, quality and findings. For example, when ii reviews had similar findings and low overlap for a detail event, the results of the reviews could be trusted despite differences in PICO scope (i.eastward. different populations or beta-lactams) or differences in dates of publication (i.e. publication dates spanned several years betwixt reviews). Alternatively, when low overlap was found betwixt reviews with inconsistent and discordant findings, discrepancies were nearly often attributed to differences in telescopic or differences in dates of review publication.

In this instance, the authors chose to use the CCA and citation matrices to appraise the influence of overlap on their overview findings. While this approach allows for a more than comprehensive information mapping exercise it also results in the potential for more reviews to be included where discrepancies in data from primary studies and discordant findings/conclusions of authors need to exist evaluated and explained.

A potential limitation of this approach is the complicated analysis of overlap by outcome. With ix clinical outcomes considered and overlap assessed for each, it may make for a cumbersome and long read for the clinician who is more interested in the bottom line. However, a complicated analysis of overlap will lead to more than comprehensive and reliable findings. When deciding whether to undertake an overview, authors should take into consideration the known or anticipated trade-offs of using different overlap methods. More empirical research well-nigh the trade-offs associated with alternative overlap methodological approaches is needed.

Discussion

Our study underlines that there is no standard methodological arroyo to bargain with overlap in primary studies beyond reviews. The level of complication when dealing with overlap tin can vary depending on the yield, trends and patterns of the included literature and the telescopic of the overview question. Choosing a method might be dependent on the number of included reviews and their primary studies. For example, visual presentations of overlap becomes more challenging with an increasing number of reviews. In reviews with high yields, the breadth and depth of analysis tin can be challenging and resource intensive. Creating large reports with also much information and data can limit the readability and utility of an overview for determination makers and healthcare providers, and decrease the efficiency in its product.

Several possible approaches to manage overlap have been illustrated by presenting six instance studies. The methodological approaches tin can exist categorized by the stages in the comport of an overview. For example, at the eligibility stride, the trade-off of authors choosing one systematic review among many is a loss of potentially of import information, which may lead to greater dubiousness about the effects of the intervention, while at the aforementioned fourth dimension removing the issue of overlap. Including all systematic reviews is probable to innovate overlap, and will pb to challenges when synthesising a large corporeality of review data (e.g. resolving discrepant quality assessments, standardising effect metrics). When including all systematic reviews, resolving these challenges is likely to be resource intensive and cumbersome for the reader. More importantly, ignoring overlap in main study data from the included reviews may affect the trustworthiness of the overview findings. If overlap is non addressed at the inclusion or information extraction steps, overview authors are brash to quantify and assess the influence of overlap at the synthesis phase of the overview.

As a general dominion, we think the creating citation matrices are helpful. Many authors detect that a citation matrix is essential to interpret the amount of overlap (e.one thousand. using the CCA). Nevertheless, better reporting of the reference review when computing overlap, and details about how overlap is calculated is needed. Visual examination of citation matrices of master studies included in reviews tin exist used to decide if low overlap is related to temporal gaps in search time frames, gaps in enquiry topics, or how studies are amassed. Smaller commendation matrices past outcome tin be adult, which volition aid in determining if overlap is an issue at the outcome level. More than sophisticated methods to present overlap to the readers can be found in Bougioukas and colleagues [33], such as upset plots, heatmaps and node-link graphs for visualizing overlap.

Interpretation of the CCA has been an issue for many authors. First, CCA calculations for all chief studies across reviews, CCA calculations between ii reviews just, and CCA calculations for ane outcome [17] yield vastly different results. Information technology may exist the case every bit in Thabet et al. that pairs of systematic reviews had high overlap only the overview at a whole resulted in low or moderate overlap. Conducting all three overlap analyses tin provide insight into which pairs of systematic reviews and outcomes have low overlap, thus helping authors highlight areas of trustworthy bear witness but is more than resource intensive.

When high overlap is found at the outcome level, simply a few methods can be used to explicate or resolve overlap. Examining potential reasons for different results or conclusions across reviews with high overlap can be highly informative and may resolve the issue. When overlap is still present and presents a problem, one review many be called for the overview synthesis. The limitations of this selection is that the one review may not represent the totality of evidence on the topic, and a loss of data may result. Statistical methods (eastward.thou. conduct sensitivity analyses, inflate the variance of the pooled meta-assay estimate) can too be used to manage overlap in primary studies beyond reviews, although these methods have not been frequently used in practice.

In general, there is a lack of empirical evidence testing these methods. We identified one study empirically evaluating the touch on of five inclusion decisions on the behave of an overview. The authors found that when overviews contain overlapping primary studies, selecting a Cochrane systematic review, as opposed to the most contempo or highest quality non-Cochrane systematic review, maximized the corporeality of outcome data included in the overview [19]. While this study makes an important contribution to the empirical methods literature for overviews, significant gaps exist in evaluation of the methods used in the majority of steps and sub-steps in the comport of an overview, specially methods used to resolve overlap. Evaluations of methods tin can provide evidence, which allows researchers to brand informed choices about the most appropriate methods to use when conducting a study.

Strengths and limitations of this study

Due to resource limitations, one author screened the studies titles/abstracts, full-text manufactures against the eligibility criteria, and extracted methods information relating to overlap. We recognise this is limitation of our report, as relevant citations could take been missed, and data errors could have been introduced. We only searched i database for relevant studies, but because (a) 2 of the authors are experts in overview methods, and follow the literature closely, and (b) nosotros did forward citation searching on a seminal paper from 2014 on overlap in overviews [thirteen], nosotros feel like nosotros have captured all relevant papers on this topic.

Conclusions

9 studies were found and mapped to the methods identified by the MOoR framework to manage overlap. Six studies were manufactures describing methods for overviews, two were guidance documents, and one was an empirical study. Several methods map beyond four steps in the behave of an overview – the eligibility criteria footstep, the data extraction step, the cess of risk of bias pace, and the synthesis step. The methods can be used across the steps in the conduct of an overview depending on the nature and scope of the topic. No one standardised methodological arroyo exists to visualise, quantify and resolve overlap in master studies across reviews.

Gaps in in evaluation of methods to accost overlap were found and further investigation in this area is needed. Evaluation of the methods used in overviews is important as policymakers and clinicians need to be confident that the methods used to carry overviews result in valid and reliable bear witness.

Availability of information and materials

All information generated or analysed during this report are included in this published article.

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There was no funding to behave this report.

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Affiliations

  1. Cochrane Hypertension Grouping and the Therapeutics Initiative, Department of Anesthesiology, Pharmacology and Therapeutics, University of British Columbia, Vancouver, Canada

    Carole Lunny

  2. Establish for Enquiry in Operative Medicine, Witten/Herdecke Academy, Cologne, Deutschland

    Dawid Pieper

  3. Hôpital Montfort, Ottawa, Canada

    Pierre Thabet

  4. The Ottawa Hospital and Ottawa Hospital Research Constitute, Ottawa, Canada

    Salmaan Kanji

Contributions

CL conceived of the study, conducted the search, all other methods and analysis, and presented 1 case written report. DP and SK presented two instance studies each, and PT presented one case study. CL drafted the start typhoon of the manuscript. All authors revising information technology critically for important intellectual content, read and approved the final manuscript.

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Correspondence to Dawid Pieper.

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Lunny, C., Pieper, D., Thabet, P. et al. Managing overlap of chief written report results across systematic reviews: practical considerations for authors of overviews of reviews. BMC Med Res Methodol 21, 140 (2021). https://doi.org/10.1186/s12874-021-01269-y

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Keywords

  • Overviews of systematic reviews
  • Meta-review
  • Overview methodology
  • Review methods
  • Reporting
  • Umbrella review
  • Evidence synthesis
  • Overlap
  • Precision

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