Which Statement About Systematic Reviews (Srs) Is Not True
Indian J Anaesth. 2016 Sep; 60(nine): 689–694.
A cursory overview of systematic reviews and meta-analyses
Kamath Sriganesh
iDepartment of Neuroanaesthesia, National Institute of Mental Health and Neurosciences, Bengaluru, Karnataka, India
Harsha Shanthanna
iiDepartment of Anesthesia, McMaster University, Hamilton, Ontario, Canada
Jason West Busse
2Department of Anesthesia, McMaster University, Hamilton, Ontario, Canada
3Section of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada
4The Michael Thousand. DeGroote Institute for Hurting Research and Care, McMaster University, Hamilton, Ontario, Canada
Abstract
Systematic reviews (SRs) are performed to acquire all evidence to accost a specific clinical question and involve a reproducible and thorough search of the literature and disquisitional appraisal of eligible studies. When combined with a meta-analysis (quantitatively pooling of results of individual studies), a rigorously conducted SR provides the best available evidence for informing clinical practice. In this article, we provide a brief overview of SRs and meta-analyses for anaesthesiologists.
Key words: Evidence-based medicine, meta-analysis, systematic review
INTRODUCTION
The showtime tenet of bear witness-based medicine (EBM) is that clinical decisions should be influenced by all relevant high-quality evidences, as opposed to select studies.[i] Systematic reviews (SRs) are aimed at acquiring all evidence to address a specific research question and involve a reproducible and thorough search of the literature and critical evaluation of eligible studies. This is different than narrative reviews, which allow authors to highlight the findings from select studies. The salient features and differences between systematic and narrative reviews are described in Table 1. At that place are several other types of reviews such equally scoping reviews, rapid reviews, systematised reviews, overviews and critical reviews, which have their own strengths and limitations.[ii] For the purposes of this overview, we will focus on SRs of therapeutic interventions.
Table ane
Differences between a narrative review and a systematic review
DEFINITIONS OF SYSTEMATIC REVIEW AND META-ANALYSIS
A rigorously performed SR identifies all empirical prove that meets pre-specified eligibility criteria to answer a specific clinical question using explicit, systematic methods to minimise bias and provides reliable findings to inform evidence-based clinical care.[three] A SR tin exist either qualitative, in which eligible studies are summarised, or quantitative (meta-analysis) when data from private studies are statistically combined. Non all SRs may result in meta-analyses. Similarly, not all meta-analyses may take been preceded past a SR, though this chemical element is essential to ensure that findings are not affected past selection bias.
PURPOSE OF SYSTEMATIC REVIEWS AND ITS POSITION IN THE HIERARCHY OF Bear witness
Large volumes of research are conducted and published every year, and at times with alien results.[4] Differences in findings lead to confusion among physicians, patients and policymakers. Resolving such situations necessitates a comprehensive and transparent synthesis of all available literature that evaluates the quality of evidence and when present, explores possible reasons for discrepancies. SRs are best suited to address such a demand, especially when combined with meta-assay. The second tenet of EBM is that there is a bureaucracy of evidence, from research designs at higher risk of bias, to report designs at lower take chances of bias.[5] Because of the advantages described in Table one, well-conducted SRs of high quality randomised controlled trials (RCTs) are placed at the highest level in the bureaucracy of evidence.[6]
COMPONENTS OF SYSTEMATIC REVIEW
Bear of a SR starts with a clinical question and a protocol with clear identification of objectives, outcomes and a well-laid out plan for analysis and reporting of results. It is highly desirable to register protocols in a publicly available database, such as PROSPERO.[7] This allows for transparency and increases confidence among readers in the report results. The stages in the behave of SRs are highlighted in the following section and a summary is provided in Table 2.
Table two
Summary of applied steps in the acquit of a systematic review
Formulating a clinical question
A specific and clearly idea out question is the first step towards completing a SR. The question is more often than not framed in the population, intervention, comparator and outcomes (PICO) format and influences the scope of review.[eight] A review with a narrow definition of PICO elements (eastward.g., issue of dalteparin on deep vein thrombosis (DVT) prophylaxis after hip replacement surgery) volition apply to a much more specific patient population than a review with broader criteria (eastward.chiliad., result of low molecular weight heparin medications on DVT prophylaxis afterwards joint replacement surgeries).
The conclusion on the blazon of study design(s) to be included, RCTs or observational studies or both, is made based on the review question. In SRs of therapeutic interventions, RCTs are desirable over observational studies. Observational report designs are considered when at that place are no RCTs, or the available RCTs are of poor quality or if the review question pertains to rare events. Information technology is non uncommon for SRs to include only English language-language articles, only this risks selection bias (English-language bias) and including non-English language manufactures is highly preferable.[ix]
A detailed review protocol that identifies report objectives, outcomes, methods of study selection, data extraction, analysis and reporting should be prepared before the conduct of the review.[10] This promotes more rigorous SRs every bit researchers are required to carefully retrieve through the details of their study before proceeding, and ensures that any deviation from the intended methodology is transparent to stakeholders. A research team consisting of one or more content experts, a medical librarian, a methodologist and a statistician, along with other stakeholders (e.g., patients) ensures the requisite skill set for pattern, conduct and reporting of the review.
Searching the literature
This procedure is ideally conducted past a research librarian. If unavailable, a librarian's assistance should exist sought to design and complete the literature search. Common medical databases for searching include Medline, Embase and the Cochrane Central Annals of Controlled Trials (CENTRAL); however, based on the research question, additional databases may exist advisable. The search strategy for a SR is based on the research question (PICO) and may vary slightly based on database-specific indexing practices; ideally, all dataset-specific search strategies will exist included as appendices when SRs are published.[10]
Literature search strategies volition typically utilise a combination of medical subject heading (MeSH) terms and free-text keywords. For example, if we are interested in the concept of anaesthesia through the breathing of gas, the MeSH term for this concept is 'Anaesthesia, Inhalation,' which will capture publications that have had this subject heading assigned to them by a database indexer. In addition, we might search in the title and abstruse field of citations for a specific free-text term. For example, a free-text phrase we might employ is 'an?esthe* adj3 (inhal* or insufflation).' The question marker will capture British or American spelling variations while the asterix will capture all variations of the root word (inhaled, inhalation, inhaling, etc.). The adjacency operator (adj3) requires that the 2 words appear within three words of ane some other so that an commodity containing a phrase such as 'anaesthesia delivered past inhalation' will exist captured. By combining the results of the ii sets of searches using the "OR" operator, a larger set of potentially relevant records is retrieved. A balance between sensitivity (capturing all possible evidence pertaining to review question) and specificity (retrieving more than relevant studies) is necessary to attain a comprehensive and practical search. Afterward removal of duplicates, a final list of citations (titles and abstracts) from all reviewed databases is compiled.
Selection of relevant studies
Based on the selection criteria, the manufactures obtained through literature search are taken through a ii-stage process of screening and selection. The first stage is carried out on titles and abstracts in which a more than sensitive strategy is adopted to clearly exclude unrelated articles. For the second phase, all potentially relevant studies are caused in full-text to complete final adjudication of eligibility. Both these stages should ideally be performed independently and in indistinguishable by teams of reviewers to provide assurances regarding reliability. Discrepancies in selection are resolved past arbitration. Consensus exercises between reviewers at the start of each stage help promote a high rate of agreement. The kappa statistic can be calculated to inform agreement betwixt reviewers, and is interpreted as follows: Most perfect agreement (0.81–0.99), substantial agreement (0.61–0.80), moderate agreement (0.41–0.60), fair agreement (0.21–0.40), slight agreement (0.01–0.20) and risk agreement (0).[eleven] At the end of this process, a last list of articles to exist included within the SR is obtained.
Data extraction
This stage involves extraction of individual written report information necessary for the analysis and reporting of the review. Extractable data will typically include report design characteristics, adventure of bias (RoB) items, participant demographic information and follow-upward and study outcomes. Like to screening, this is performed independently past paired reviewers to avoid errors in the acquisition of information. Clear arrangement and recording of the extracted data are necessary to facilitate a review. Missing or unclear data items should be sought from the authors of studies and if unavailable, should be clearly documented. The apply of web-based SR software such as DistillerSR™ (http://distillercer.com/), particularly for large reviews, helps promote faster, more than organised and efficient report selection and information extraction.
Appraisal of study reporting quality
The reporting quality of a study considers the extent to which aspects of a study's design and conduct are likely to protect confronting systematic error (deviation from the truth). Systematic errors broadly autumn into iii domains of choice, measurement and confounding biases. Several tools are bachelor for cess of the methodological quality of included studies such as the Newcastle-Ottawa scale for non-randomised studies,[12] and the Cochrane RoB tool for RCTs.[thirteen] Quality cess is required for interpreting results and for grading the strength of evidence. An example of assessing and representing the RoB in private studies and across studies is available in the cited reference.[xiv]
Data synthesis (meta-analysis)
It is desirable to explicitly country how data will be synthesised a priori to avert data mining, and to reduce unsubstantiated claims during the synthesis.[15] Unlike study designs and event measures should exist summarised and synthesised separately.
Meta-analysis is a statistical technique used for combining the effect on a common outcome domain (due east.chiliad., hurting relief) across individual studies. By combining study results, the precision associated with a handling result becomes narrower.[3] Findings from meta-analyses are graphically depicted in the form a forest plot [Figure one],[xiv] with private studies and their handling result represented horizontally. The vertical line indicates the line of null outcome, and furnishings either to the left or correct of the line indicate the benefit of the intervention or command therapy. Individual study event sizes are shown as a square forth with the associated 95% conviction interval, and the pooled judge is shown as a diamond.
Forest plot depicting the use of rescue analgesia in the early on mail service-operative flow in caudal and non-caudal regional techniques in children undergoing inguinal surgeries. Harsha Shanthanna, Balpreet Singh, and Gordon Guyatt, "A Systematic Review and Meta-Analysis of Caudal Block as Compared to Noncaudal Regional Techniques for Inguinal Surgeries in Children," BioMed Research International, vol. 2014, Article ID 890626, 17 pages, 2014. doi:ten.1155/2014/890626
For continuous outcomes that are reported using the aforementioned musical instrument across trials, the pooled estimate can be reported in natural units as a weighted mean difference. The more common situation is that trials eligible for meta-analysis volition report outcomes tapping into the same domain (e.g., pain) using different instruments. In such cases, the effect estimates crave standardisation before pooling. A mutual approach is to catechumen different instruments into standard divergence units, and report the pooled effect as a standardised hateful divergence (SMD) (a value of 0.ii represents a modest difference, 0.v a medium departure and 0.8 a large departure in treatment result). However, the SMD is hard for patients and clinicians to interpret and is vulnerable to baseline heterogeneity of trial patients: greater heterogeneity among pain scores at baseline will effect in a smaller SMD versus studies that enrol patients that provide more than homogeneous scores, even when the truthful underlying effect is the aforementioned. We have previously published guidance regarding approaches that can be used to puddle different instruments in natural units, minimally important deviation units, a ratio of ways, or the odds or risk of achieving a patient-important level of improvement.[16] For binary outcomes, pooled treatment furnishings are typically expressed as an odds ratio or risk ratio.
Pooled treatment effects may demonstrate heterogeneity suggesting that an overall pooled result may be misleading as handling effects differ between studies. The statistical evidence of heterogeneity tin be estimated using Cochrane's Q-test (heterogeneity detected if P ≤ 0.10), and the I2 statistic (a percentage measure of inconsistency) - college I2 indicates more heterogeneity, hence higher inconsistency.[17] A crude guide for interpreting heterogeneity using the I2 statistic is as follows: 0%–twoscore%, insignificant; thirty%–60%, moderate; l%–ninety%, meaning and 75%–100%, considerable. If heterogeneity is high, it would non necessarily mean abandoning meta-analyses, merely caution should be exercised during interpretation of results. Strategies to explore heterogeneity include subgroup analysis (exploring outcomes for predefined subgroups, based on PICO, or RoB, etc.) or meta-regression (predicting outcome according to one or more continuous explanatory variables).[eighteen]
The force of a SR is the abstention of selection bias, strengths of meta-analysis include an increase in power that improves statistical precision of treatment result estimates, and the ability to explore for subgroup furnishings (although betwixt-study subgroup effects are less credible than within-study subgroup effects). The main limitation of SRs and meta-assay are related to the quality of included studies – aggregating poor quality studies will lead to a poor quality review.
Reporting the findings
The reporting of SRs should be guided by the preferred reporting items for SR and meta-analysis (PRISMA) for RCTs[19] and Meta-analysis of observational studies in epidemiology (MOOSE) for observational data.[xx] The grading of recommendations assessment, evolution and evaluation (GRADE) arroyo should be used to evaluate and study the quality of evidence for each outcome reported in a SR (http://world wide web.gradeworkinggroup.org). Resource such as the Cochrane Database of SRs[21] provide access to high-quality SRs on treatment interventions.
SUMMARY
There are 3 tenets of EBM: (1) all relevant evidence should be considered to inform clinical conclusion-making, (2) at that place is a hierarchy of testify that is based on the ability of different study designs to address RoB and (3) prove solitary is never enough (due east.g., patient values and preferences). Rigorously conducted SRs and meta-analyses present an invaluable strategy to address the ist 2 of these tenants, and are essential to the do of EBM.
Financial support and sponsorship
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Conflicts of interest
There are no conflicts of interest.
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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5037953/
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