Formulating research questions – A systematic review attempts to gather all available empirical research by using clearly defined, systematic methods to obtain answers to a specific question. A meta-analysis is the statistical process of analyzing and combining results from several similar studies.
Here, the definition of the word “similar” is not made clear, but when selecting a topic for the meta-analysis, it is essential to ensure that the different studies present data that can be combined. If the studies contain data on the same topic that can be combined, a meta-analysis can even be performed using data from only two studies.
However, study selection via a systematic review is a precondition for performing a meta-analysis, and it is important to clearly define the Population, Intervention, Comparison, Outcomes (PICO) parameters that are central to evidence-based research.
Why use systematic reviews and meta-analysis?
Summary – A systematic review is an overview of primary studies which contains an explicit statement of objectives, materials, and methods, and has been conducted according to explicit and reproducible methodology. A meta-analysis is a mathematical synthesis of the results of two or more primary studies that addressed the same hypothesis in the same way.
- Although meta-analysis can increase the precision of a result, it is important to ensure that the methods used for the reviews were valid and reliable.
- High-quality systematic reviews and meta-analyses take great care to find all relevant studies, critically assess each study, synthesize the findings from individual studies in an unbiased manner, and present balanced important summary of findings with due consideration of any flaws in the evidence.
Systematic review and meta-analysis is a way of summarizing research evidence, which is generally the best form of evidence, and hence positioned at the top of the hierarchy of evidence. Systematic reviews can be very useful decision-making tools for primary care/family physicians.
Can you do a meta-analysis without a systematic review?
What Is A Meta-Analysis? – A meta-analysis is a statistical procedure used to summarize data from multiple studies. It’s done in the context of systematic reviews, representing a specialized subset. In other words, a meta-analysis is simply an approach done within a systematic review to combine the data derived for it.
What is a review or meta-analysis?
Meta-analysis is a systematic review of a focused topic in the literature that provides a quantitative estimate for the effect of a treatment intervention or exposure.
What level is a systematic review and meta-analysis?
Levels of evidence (sometimes called hierarchy of evidence) are assigned to studies based on the methodological quality of their design, validity, and applicability to patient care. These decisions gives the “grade (or strength) of recommendation.”
| Level of evidence (LOE) | Description |
| Level I | Evidence from a systematic review or meta-analysis of all relevant RCTs (randomized controlled trial) or evidence-based clinical practice guidelines based on systematic reviews of RCTs or three or more RCTs of good quality that have similar results. |
| Level II | Evidence obtained from at least one well-designed RCT (e.g. large multi-site RCT). |
| Level III | Evidence obtained from well-designed controlled trials without randomization (i.e. quasi-experimental). |
| Level IV | Evidence from well-designed case-control or cohort studies. |
| Level V | Evidence from systematic reviews of descriptive and qualitative studies (meta-synthesis). |
| Level VI | Evidence from a single descriptive or qualitative study. |
| Level VII | Evidence from the opinion of authorities and/or reports of expert committees. |
This level of effectiveness rating scheme is based on the following: Ackley, B.J., Swan, B.A., Ladwig, G., & Tucker, S. (2008). Evidence-based nursing care guidelines: Medical-surgical interventions. (p.7), St. Louis, MO: Mosby Elsevier. Different types of clinical questions are best answered by different types of research studies.
| Clinical Question | Suggested Research Design(s) |
| All Clinical Questions | Systematic review, meta-analysis |
| Therapy | Randomized controlled trial (RCT), meta-analysis Also: cohort study, case-control study, case series |
| Etiology | Randomized controlled trial (RCT), meta-analysis, cohort study Also: case-control study, case series |
| Diagnosis | Randomized controlled trial (RCT) Also: cohort study |
| Prevention | Randomized controlled trial (RCT), meta-analysis Also : prospective study, cohort study, case-control study, case series |
| Prognosis | Cohort study Also: case-control study, case series |
| Meaning | Qualitative study |
| Quality Improvement | Randomized controlled trial (RCT) Also: qualitative study |
| Cost | Economic evaluation |
What is an example of a meta-analysis?
A meta-analysis example as applied to the medical field might attempt to measure the change in depression symptoms over a given period of time between a test group taking a given anti-depressant and a control group that does not take the medication.
What is the purpose of a meta-analysis?
Meta-Analysis and Systematic Review – Glass first defined meta-analysis in the social science literature as “The statistical analysis of a large collection of analysis results from individual studies for the purpose of integrating the findings” 9, Meta-analysis is a quantitative, formal, epidemiological study design used to systematically assess the results of previous research to derive conclusions about that body of research.
- Typically, but not necessarily, the study is based on randomized, controlled clinical trials.
- Outcomes from a meta-analysis may include a more precise estimate of the effect of treatment or risk factor for disease, or other outcomes, than any individual study contributing to the pooled analysis.
- Identifying sources of variation in responses; that is, examining heterogeneity of a group of studies, and generalizability of responses can lead to more effective treatments or modifications of management.
Examination of heterogeneity is perhaps the most important task in meta-analysis. The Cochrane collaboration has been a long-standing, rigorous, and innovative leader in developing methods in the field 10, Major contributions include the development of protocols that provide structure for literature search methods, and new and extended analytic and diagnostic methods for evaluating the output of meta-analyses.
Use of the methods outlined in the handbook should provide a consistent approach to the conduct of meta-analysis. Moreover, a useful guide to improve reporting of systematic reviews and meta-analyses is the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-analyses) statement that replaced the QUOROM (QUality Of Reporting of Meta-analyses) statement 11 – 13,
Meta-analyses are a subset of systematic review. A systematic review attempts to collate empirical evidence that fits prespecified eligibility criteria to answer a specific research question. The key characteristics of a systematic review are a clearly stated set of objectives with predefined eligibility criteria for studies; an explicit, reproducible methodology; a systematic search that attempts to identify all studies that meet the eligibility criteria; an assessment of the validity of the findings of the included studies (e.g., through the assessment of risk of bias); and a systematic presentation and synthesis of the attributes and findings from the studies used.
- Systematic methods are used to minimize bias, thus providing more reliable findings from which conclusions can be drawn and decisions made than traditional review methods 14, 15,
- Systematic reviews need not contain a meta-analysisthere are times when it is not appropriate or possible; however, many systematic reviews contain meta-analyses 16,
The inclusion of observational medical studies in meta-analyses led to considerable debate over the validity of meta-analytical approaches, as there was necessarily a concern that the observational studies were likely to be subject to unidentified sources of confounding and risk modification 17,
Pooling such findings may not lead to more certain outcomes. Moreover, an empirical study showed that in meta-analyses were both randomized and non-randomized was included, nonrandomized studies tended to show larger treatment effects 18, Meta-analyses are conducted to assess the strength of evidence present on a disease and treatment.
One aim is to determine whether an effect exists; another aim is to determine whether the effect is positive or negative and, ideally, to obtain a single summary estimate of the effect. The results of a meta-analysis can improve precision of estimates of effect, answer questions not posed by the individual studies, settle controversies arising from apparently conflicting studies, and generate new hypotheses.
Which is better systematic review or meta-analysis?
??♀️ What does ‘systematic’ actually mean? – In this context, systematic means that the methods used to search for and analyse the data are transparent, reproducible and defined before searching begins. This is what differentiates a systematic review from a descriptive review that might be based on, for example, a subset of the literature that the author is familiar with at the time of writing.
Systematic reviews strive to be as thorough and rigorous as possible to minimise the bias that would result from cherry-picking studies in a non-systematic way. Systematic reviews sit at the top of the evidence hierarchy because it is widely agreed that studies with rigorous methods are those best able to minimise the risk of bias on the results of the study.
This is what makes systematic reviews the most reliable form of evidence (see figure 2). 
Figure 2: Systematic reviews are considered to be the gold standard of scientific evidence
When should you not do meta-analysis?
Mixing apples and oranges – Two main criticisms of meta-analysis are that it combines different types of studies (“mixing apples and oranges”), and that the summary effect may ignore important differences between studies. Meta-analysis should be avoided if studies are too heterogeneous to be comparable, as the metaanalytical results may be meaningless and true effects may be obscured.
What type of research is a systematic review?
Request Permissions – If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.
- A high-quality systematic review is described as the most reliable source of evidence to guide clinical practice.
- The purpose of a systematic review is to deliver a meticulous summary of all the available primary research in response to a research question.
- A systematic review uses all the existing research and is sometime called ‘secondary research’ (research on research).
They are often required by research funders to establish the state of existing knowledge and are frequently used in guideline development. Systematic review findings are often used within the View Full Text
How do you tell if an article is a systematic review?
Journal List J R Soc Med v.96(3); 2003 Mar PMC539417
As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with, the contents by NLM or the National Institutes of Health. Learn more about our disclaimer. J R Soc Med.2003 Mar; 96(3): 118–121.
Systematic reviews and meta-analyses are a key element of evidence-based healthcare, yet they remain in some ways mysterious. Why did the authors select certain studies and reject others? What did they do to pool results? How did a bunch of insignificant findings suddenly become significant? This paper, along with a book 1 that goes into more detail, demystifies these and other related intrigues.
A review earns the adjective systematic if it is based on a clearly formulated question, identifies relevant studies, appraises their quality and summarizes the evidence by use of explicit methodology. It is the explicit and systematic approach that distinguishes systematic reviews from traditional reviews and commentaries.
What is the difference between a systematic review and a review?
The kind of review to be conducted depends on the intended purpose of the research. Literature reviews usually answer broad and descriptive research questions. Systematic reviews are more comprehensive and precise because they seek to answer specific scientific questions of high importance.
Can a paper be a systematic review and meta-analysis?
Key Terms Defined – Systematic reviews differ from traditional narrative reviews in several ways. Narrative reviews tend to be mainly descriptive, do not involve a systematic search of the literature, and thereby often focus on a subset of studies in an area chosen based on availability or author selection.
Thus narrative reviews while informative, can often include an element of selection bias. They can also be confusing at times, particularly if similar studies have diverging results and conclusions. Systematic reviews, as the name implies, typically involve a detailed and comprehensive plan and search strategy derived a priori, with the goal of reducing bias by identifying, appraising, and synthesizing all relevant studies on a particular topic.
Often, systematic reviews include a meta-analysis component which involves using statistical techniques to synthesize the data from several studies into a single quantitative estimate or summary effect size (Petticrew & Roberts, 2006). In contrast to traditional hypothesis testing which can give us information about statistical significance (i.e., did the intervention group differ from the control group) but not necessarily clinical significance (i.e., was this difference clinically meaningful or large), effect sizes measure the strength of the relationship between two variables, thereby providing information about the magnitude of the intervention effect (i.e., small, medium, or large).
The type of effect size calculated generally depends on the type of outcome and intervention being examined as well as the data available from the published trials; however, some common examples include odds ratios (OR), weighted/standardized mean differences (WMD, SMD), and relative risk or risk ratios (RR).
Although systematic reviews are published in academic forums, there are also organizations and databases specifically developed to promote and disseminate them. For example, the Cochrane Collaboration ( www.cochrane.org ) is a widely recognized and respected international and not-for-profit organization that promotes, supports, and disseminates systematic reviews and meta-analyses on the efficacy of interventions in the health care field.
How many studies are needed for a meta-analysis?
Two studies is a sufficient number to perform a meta-analysis, provided that those two studies can be meaningfully pooled and provided their results are sufficiently ‘similar’.
Is a meta-analysis an empirical study?
But how do you identify empirical research? Empirical research is typically published in scholarly journals. But not everything in scholarly journals is necessarily empirical research – you still need to carefully evaluate the methods of the article to determine if it is empirical research.1. 
2. Look out for types of articles that are NOT empirical. Meta-analyses, literature reviews (with no other study components), editorials/letters, book reviews, case studies, opinions. 
3. In some databases, such as PsycINFO, you can limit to empirical research under Methodology in the “Advanced Search” section. Or limit to evidence-based practice” in CINAHL. 
4. In other databases, try using keywords such as empirical research, quantitative method, qualitative method, survey, ethnography, fieldwork or other type of empirical research method.
What tool is used for meta-analysis?
Screening Tools for Evaluating Studies revtools is an R package to support article screening for evidence synthesis. It provides a free, easy-to-use, open-source environment to conduct your literature review or meta-analysis.
What are the two types of meta-analysis?
10.4 Meta-analysis of dichotomous outcomes – There are four widely used methods of meta-analysis for dichotomous outcomes, three fixed-effect methods (Mantel-Haenszel, Peto and inverse variance) and one random-effects method (DerSimonian and Laird inverse variance).
What is a meta-analysis for dummies?
Meta-Analysis A subset of systematic reviews; a method for systematically combining pertinent qualitative and quantitative study data from several selected studies to develop a single conclusion that has greater statistical power. This conclusion is statistically stronger than the analysis of any single study, due to increased numbers of subjects, greater diversity among subjects, or accumulated effects and results.
To establish statistical significance with studies that have conflicting results To develop a more correct estimate of effect magnitude To provide a more complex analysis of harms, safety data, and benefits To examine subgroups with individual numbers that are not statistically significant
If the individual studies utilized randomized controlled trials (RCT), combining several selected RCT results would be the highest-level of evidence on the evidence hierarchy, followed by systematic reviews, which analyze all available studies on a topic.
What is the biggest benefit of meta-analyses?
Benefits of meta-analysis – A meta-analysis has many benefits. By combining results into one large study, it reduces the time and energy that decision-makers spend looking at research. But the real benefit lies in the way meta-analysis can make sense of inconclusive and conflicting data from each original study.
- Through meta-analysis, researchers can combine smaller studies, essentially making them into one big study, which may help show an effect.
- Additionally, a meta-analysis can help increase the accuracy of the results.
- This is also because it is, in effect, increasing the size of the study.
- By helping to bring into focus the sometimes blurry picture developing from the abundance of research evidence on any given topic, a meta-analysis is a very effective type of review.
Source: At Work, Issue 48, Spring 2007 : Institute for Work & Health, Toronto
What are the strengths of systematic review and meta-analysis?
Strengths – As previously mentioned, systematic reviews are considered by many to be the gold standard of evidence synthesis. There are several good reasons for this:
- Systematic reviews utilize rigorous methods which aim to minimize bias in the review of evidence from individual studies.
- Systematic reviews attempt to be comprehensive in their search strategy, enabling reviewers to look at all of the available evidence and combine it accordingly.
- Systematic reviews, when paired with an appropriately conducted meta-analysis, can allow reviewers to better understand the efficacy and effect size of a given intervention, analyze safety risks and benefits more comprehensively, extrapolate findings to the larger population, and examine sub-populations.
- Systematic reviews tend to include only trials of high-quality, such as randomized controlled trials (RCTs), however, systematic reviews are conducted on other types of studies.
- Systematic reviews are often conducted using standardized quality-assurance practices and guidelines such as PRISMA, the Cochrane Handbook for Systematic Reviews, and GRADE.
Given all of the above, it is easy to see why systematic reviews have been relied upon for decades as a source of evidence-based answers to questions that critically affect the practice of researchers, clinicians, or practitioners.
Which is an advantage of meta-analysis compared to narrative systematic reviews?
Advantages and disadvantages of the meta-analysis approach – PubMed ADVANTAGES OF META-ANALYSIS: Literature reviews have traditionally been largely narrative. Meta-analysis now offers the opportunity to critically evaluate and statistically combine results of comparable studies or trials.
- Its major purposes are to increase the numbers of observations and the statistical power, and to improve the estimates of the effect size of an intervention or an association.
- Methods: There is, as yet, no unanimously accepted strategy for performing a meta-analysis but researchers agree that each meta-analysis should be conducted like a scientific experiment and begin with a protocol, which clearly states its aim and methodology.
Meta-analysts disagree on the criteria for inclusion or exclusion of primary studies, with relation to publication status, comparability and required scientific quality, but sensitivity analyses make it possible to assess the impact of various selection criteria on the results.
Several statistical methods have been developed to analyse data extracted from the literature; more recently, meta-analyses have also been performed on individual subject data. Conclusions: Meta-analysis is superior to narrative reports for systematic reviews of the literature, but its quantitative results should be interpreted with caution even when the analysis is performed according to rigorous rules.
: Advantages and disadvantages of the meta-analysis approach – PubMed
What is the difference between a meta-analysis and a meta synthesis systematic review?
In summary, a meta-analysis is a way of testing a hypothesis whereas a meta-synthesis is a way of developing a new theory.