systematic review and meta analysis pdf

Systematic Review And Meta Analysis Pdf

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Image: David Parmenter's Shop. Recommended readings:. Consult these manuals frequently at every step of your review:.

Appraising Systematic Reviews and Meta-analyses

Crowther; Systematic review and meta-analysis methodology. Blood ; 17 : — Systematic reviews and meta-analyses are being increasingly used to summarize medical literature and identify areas in which research is needed.

Systematic reviews limit bias with the use of a reproducible scientific process to search the literature and evaluate the quality of the individual studies. If possible the results are statistically combined into a meta-analysis in which the data are weighted and pooled to produce an estimate of effect.

This article aims to provide the reader with a practical overview of systematic review and meta-analysis methodology, with a focus on the process of performing a review and the related issues at each step. The average hematologist is faced with increasingly large amounts of new information about hematologic disease.

This ranges from the latest findings of complex molecular studies to results from randomized controlled trials RCTs to case reports of possible therapies for very rare conditions. With this vast amount of information being produced in published journals, presentations at conferences, and now increasingly online, it is virtually impossible for hematologists to keep up to date without many hours being spent searching and reading articles.

Review articles traditionally provide an overview of a topic and summarize the latest evidence, thus reducing the time clinicians would need to spend performing literature searches and interpreting the primary data.

These review articles, known as narrative reviews, typically address a broad number of issues related to a topic. The data are usually summarized but not statistically combined qualitative summary , and key studies are highlighted. The inferences made from narrative reviews may be, but are not necessarily, evidence based.

Narrative reviews are useful for obtaining a broad overview of a topic, usually from acknowledged experts. However, narrative reviews are susceptible to bias if a comprehensive literature search is not performed, or if only selected data are presented which conveys the author's views on a particular topic.

Systemic reviews aim to reduce bias with the use of explicit methods to perform a comprehensive literature search and critical appraisal of the individual studies. Thus, in contrast to narrative reviews, systematic reviews pose a defined clinical question. The process of performing the literature search and the specific inclusion and exclusion criteria used for study selection are described.

The quality of the included studies is formally appraised. The data are summarized, and, if the data are statistically combined quantitative summary , the systematic review is referred to as a meta-analysis.

The inferences made from systematic reviews are usually evidence based. In view of the increasing number of systematic reviews published, we feel it is important to discuss the methodology of the systematic review to allow readers to better appreciate and critically appraise systematic reviews that may be relevant for their practice.

The findings of systematic reviews can be included in the introduction of scientific papers and are increasingly performed for grant applications to summarize what is known about a topic and highlight areas in which research is needed. Having the knowledge to appraise a systematic review is an important skill, because systematic reviews are considered to be the study design with the highest level of study quality.

Although many studies are labeled as systematic reviews, this does not necessarily indicate that the study itself is of high quality because any group of studies can be subject to a systematic review, and data can almost always be combined in a meta-analysis. The important issue is identifying if the systematic review was conducted in a manner that is replicable and free of bias, and if a meta-analysis was performed whether the data were appropriately combined.

The objective of this article is to provide a practical approach to preparing and critically appraising a systematic review. A modified version of the Quality of Reporting of Meta-analyses statement is presented in Table 1. Modified from Moher et al. What is the clinical question that needs to be answered? A careful articulation of the question is critical, because it provides the scope of the review by defining the type of patients, intervention, comparator, and outcomes evaluated in the review.

Thus, a systematic review on the use of colony-stimulating factors in patients with hematologic malignancies will be a far greater undertaking than a systematic review of colony-stimulating factors in preventing chemotherapy-induced febrile neutropenia in children with acute lymphoblastic leukemia. A major cause of bias in a systematic review is answering a different question to that originally asked.

The completeness of the search strategy will determine the comprehensiveness of the review. The more exhaustive the search the greater the effort required to produce the systematic review, but the resulting review is generally of higher quality. The development of an inclusive search strategy requires expertise, and, unless the investigator is skilled in literature searches, the help of an experienced librarian is invaluable and strongly recommended.

It is recommended that the search be performed in duplicate, because one person, especially if he or she is screening thousands of studies, may miss relevant studies. The literature search usually involves searching the following source. Many readers may remember the published Index Medicus in which journal articles were indexed based on topic. This has since been replaced by several electronic, Web-based, searchable databases.

The database to be used depends on what area of medicine the search is to be performed in. Examples of commonly used databases are shown in Table 2. Many papers are presented at conferences before publication. It can take years for the content of these abstracts to be published. Conference abstracts can be searched and evidence can be extracted before full publication. The abstracts themselves may provide sufficient data to be included in the systematic review or, if a significant publication is anticipated, may warrant contacting the abstract author to obtain information.

There are advantages and disadvantages to including conference abstracts. Studies that show inconclusive or negative results for an intervention are less likely to be published in journals but may be published in abstract form. However, abstract results often differ significantly from the final publication, and abstracts have not generally undergone the rigorous peer review process required for most journal articles.

This increases the likelihood that bias will influence the results of the systematic review. The introduction and discussion section of relevant studies may provide additional references on a subject that may have been missed by the search strategy. It is recommended that authors manually search the reference lists of found studies as a final check that no studies have been missed. One can also manually search journals in which studies on the subject of the review are likely to be published.

Writing to investigators active in the area may provide results of studies yet to be presented or published, but care must be taken with this information because it has not undergone any review process. Furthermore, most investigators will be hesitant to provide unpublished information because its inclusion in a systematic review may hamper subsequent publication.

Perhaps the greatest utility of inquiring with investigators is gaining knowledge of studies about to be published, and when delaying the systematic review will allow inclusion of these articles and thus make the review more timely. Investigators may also be contacted if clarification of published information is required.

Apart from the searchable databases discussed earlier, there are other useful resources online. These include registers of clinical trials eg, www. Searching the Internet with the use of search engines such as Google provides a user-friendly method to obtain information, but it is not recommended for systematic reviews because the accuracy of the information on the Internet is not ensured. Internet searches are notoriously nonspecific, and much time may be spent without much gain; this highlights the advantages of seeking input from a professional librarian before initiating a search.

Several decisions need to be made with regard to the search strategy. Investigators must decide what databases are to be searched, the level of detail in the search strategy, and whether the search should be done in duplicate. The search will produce a large number of possible studies, many of which can be excluded on the basis of their title and abstract.

However, more detailed review of individual studies is required for those studies passing the initial screen. When appraising a review, the reader should assess the completeness of the literature search. All relevant databases should be searched, and the search terms should be scrutinized for alternate terms or alternate spellings.

The reader should also assess if the search strategy could have excluded relevant studies by being too specific. It is best to establish, a priori, inclusion and exclusion criteria for accepting studies.

These criteria should be explicit, and the most rigorous reviews should record the specific reasons for including or excluding all studies identified in the literature search. Specific recording for each study not only reduces the risk of bias but also allows rapid reassessment should the rationale for exclusion of one or more studies be called into question.

Selecting studies in duplicate can help ensure that the correct studies are included and relevant studies are not missed. Deciding which studies to include or exclude in the review is very important. Inclusion or exclusion is usually based on the following different reasons. The quality of the systematic review or meta-analysis is based in part on the quality of the included studies. RCTs have a lower potential for bias compared with observational studies.

Generally, RCTs studies in which participants are randomly assigned to an intervention are intrinsically of better quality than nonrandomized studies in which participants are given an intervention then compared with another group that is similar but did not receive the intervention that in turn are better than case series or case reports.

The randomization process should equally distribute measurable and unmeasurable confounding factors between the 2 groups. As a result, differences observed should be due to the intervention rather than their occurring as a result of the effect of differences between those patients receiving the experimental, and those receiving the control, intervention. Given the reduced likelihood for bias, many systematic reviews only include RCTs; nonrandomized data are only included if randomized data are not available.

It is important to note that even if the systematic review is based on randomized data, this does not ensure that the review itself is of high quality or that definitive conclusions can be made. Limiting studies by language will reduce the number of studies needed to review, especially if there is difficulty in translating a study.

This may be acceptable for many reviews, but in some areas there may be many important studies published in other languages. Consequently, excluding studies on the basis of language must be done with care. For example, Chagas disease is endemic in Latin America, and a systematic review of transfusion-transmitted Chagas disease limited to English-only publications will exclude potentially important studies. Limiting studies by date can be done if data does not exist before a specific date.

For example, imatinib mesylate Gleevec for treatment of chronic myeloid leukemia was developed in the s with phase 1 clinical trial data emerging by the end of the decade. Hence, a systematic review that involves imatinib would not require a literature search earlier than Some studies publish interim data or use the same patient cohorts in multiple publications. Excluding duplicate studies will eliminate overrepresentation of that particular data in the systematic review.

An example of inclusion and exclusion criteria for studies to be included in a systematic review of colony-stimulating factor use for the prevention of adverse effects in the treatment of lymphoma. The quality of the studies included in the systematic review determines the certainty with which conclusions can be drawn, based on the summation of the evidence. Consequently, once all the relevant studies have been identified, the studies should undergo a quality assessment.

This is particularly important if there is contradictory evidence. As with study selection, quality assessment performed in duplicate can help to minimize subjectivity in the assessment. Various tools are designed for performing study quality assessment. The important features in a quality assessment of RCTs include the following:. The participants are not highly selected and are similar to those found in normal clinical practice content validity. Neither the participants nor the researchers are able to tell how patients will be allocated before random assignment allocation concealment.

M.Sc. Course Material - Systematic Reviews

If your institution subscribes to this resource, and you don't have a MyAccess Profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus. Please consult the latest official manual style if you have any questions regarding the format accuracy. In the previous chapter Chapter 22 , The Process of a Systematic Review and Meta-analysis , we provided guidance on how to evaluate the credibility of the process of a systematic review with or without a meta-analysis. In this chapter, we address how—if the systematic review is sufficiently credible—to decide on the degree of confidence in the estimates that the evidence warrants. As you will see, systematic review authors may have conducted a credible review and analysis and one may still have little confidence in the estimates of effect.

Bigby M, Williams H. Appraising Systematic Reviews and Meta-analyses. Arch Dermatol. A systematic review is an overview that answers a specific clinical question and contains a thorough, unbiased search of the relevant literature, explicit criteria for assessing studies, and a structured presentation of the results. Many systematic reviews incorporate a meta-analysis, ie, a quantitative pooling of several similar studies to produce an overall summary of treatment effect. Meta-analysis has been criticized for the discrepancies between its findings and those of large clinical trials.

To inform evidence-based practice in health care, guidelines and policies require accurate identification, collation, and integration of all available evidence in a comprehensive, meaningful, and time-efficient manner. Approaches to evidence synthesis such as carefully conducted systematic reviews and meta-analyses are essential tools to summarize specific topics. Unfortunately, not all systematic reviews are truly systematic, and their quality can vary substantially. Since well-conducted evidence synthesis typically involves a complex set of steps, we believe formulating a cohesive, step-by-step guide on how to conduct a systemic review and meta-analysis is essential. While most of the guidelines on systematic reviews focus on how to report or appraise systematic reviews, they lack guidance on how to synthesize evidence efficiently. To facilitate the design and development of evidence syntheses, we provide a clear and concise, step guide on how to perform a systematic review and meta-analysis of observational studies and clinical trials.

A step by step guide for conducting a systematic review and meta-analysis with simulation data

Crowther; Systematic review and meta-analysis methodology. Blood ; 17 : — Systematic reviews and meta-analyses are being increasingly used to summarize medical literature and identify areas in which research is needed.

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Corpus ID: Systematic reviews and meta-analyses: an illustrated, step-by-step guide. Pai and Michael McCulloch and J.

Systematic reviews and meta-analyses present results by combining and analyzing data from different studies conducted on similar research topics. In recent years, systematic reviews and meta-analyses have been actively performed in various fields including anesthesiology. These research methods are powerful tools that can overcome the difficulties in performing large-scale randomized controlled trials. However, the inclusion of studies with any biases or improperly assessed quality of evidence in systematic reviews and meta-analyses could yield misleading results.

Systematic Review

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Introduction to systematic review and meta-analysis

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