Systematic review - Wikipedia

 

systematic literature reviews

Systematic reviews are characterised by being objective, systematic, transparent and replicable. They involve a systematic search process to locate studies which address a particular research question, as well as a systematic presentation and synthesis of the characteristics and findings of Cited by: In this way, systematic reviews are able to summarise the existing clinical research on a topic. The review plan. Review authors set about their task very methodically following, step by step, an advance plan called a protocol. The protocol describes the steps that will be followed when preparing a review. Cochrane protocols are published in. Lesson 1: Introduction to Systematic Literature reviews 🕑 37 minutes. Welcome! This lesson will give you an overview of Systematic Literature Reviews and how they can create lasting impact and inform clinical practice. Learn the basics of SLRs, their benefits and challenges, and how they are conducted.


Conducting a systematic literature search - Students 4 Best Evidence


Because of the rising number of scientific publications, it is important systematic literature reviews have a means of jointly summarizing and assessing different studies on a single topic. Systematic literature reviews, meta-analyses of published data, and meta-analyses of individual data pooled reanalyses are now being published with increasing frequency.

We here describe the essential features of these methods and discuss their strengths and weaknesses. This article is based on a selective literature search. Systematic literature reviews different types of review and meta-analysis are described, the methods used in each are outlined so that they can be evaluated, and a checklist is given for the assessment of reviews and meta-analyses of scientific articles, systematic literature reviews.

Systematic literature reviews provide an overview of the systematic literature reviews of research on a given topic and enable an assessment of the quality of individual studies.

They also allow the results of different studies to be evaluated together when these are inconsistent. Meta-analyses additionally allow calculation of pooled estimates of an effect, systematic literature reviews.

The different types of review and meta-analysis are discussed with examples from the literature on one particular topic. Systematic literature reviews and meta-analyses enable the research findings and treatment effects obtained in different individual studies to be summed up and evaluated.

Every year, there is a great increase in the number of scientific publications. For example, the literature database PubMed registered new publications inwith in and in research in Medline, last updated in January These figures make it clear how increasingly difficult it is for physicians in private practice, clinicians and scientists to obtain comprehensive current information on any given medical topic. This is why it is necessary to summarize and critically analyze individual studies on the same theme.

Summaries of individual studies are mostly prepared when the results of individual studies are unclear or inconsistent. They are also used to study relationships for which the individual studies do not have adequate statistical power, as the number of cases is too low 1, systematic literature reviews. The Cochrane Collaboration undertakes systematic processing and summary of the primary literature for many therapeutic topics, particularly randomized clinical studies www.

They have published a handbook for the performance of systematic reviews and meta-analyses of randomized clinical studies 2. Cook et al. Instructions of this sort help to lay down standards for the summary of individual studies. Guidelines have also been drawn up for the publication of meta-analyses on randomized clinical studies 4 and on observational studies 5.

Publications on individual studies may be summarized in various forms 16 — 10 :. These terms are often not clearly allocated in the literature, systematic literature reviews. The aim of the present article is to describe and distinguish these forms and to allow the reader to perform systematic literature reviews critical analysis of the results of individual studies and the quality of the systematic review or meta-analysis. The various types of systematic reviews and meta-analyses of scientific articles will be defined and the procedure will be explained.

A selective literature search was performed for this purpose. A "review" is the qualitative summary of the results of individual studies 1, systematic literature reviews. A distinction is made between narrative reviews and systematic reviews table 1. Narrative reviews A mostly provide a broad overview of a specific topic 1 They are therefore a good way of rapidly obtaining current information on research on a given topic.

However, the articles to be included are selected subjectively and unsystematically 1 Narrative reviews will not be further discussed in this article.

In contrast, systematic review articles B claim that, if systematic literature reviews, they consider all published studies on a specific theme—after the application of previously defined inclusion and exclusion criteria The aim is to extract relevant information systematically from the publications. What is important is to analyze the methodological quality of the included publications and to investigate the reasons for any differences between the results in the different studies.

The results of each study are presented and analyzed according to defined criteria, such as study design and mode of recruitment. The same applies to the meta-analysis of published data C. In addition, the results are quantitatively summarized using statistical methods and pooled effect estimates glossary are calculated 1. Systematic literature reviews confounder is a factor which is linked to both the studied disease and the studied exposure.

For this reason, it can either enhance or weaken the true association between the disease and the target parameter. An effect estimate, such as the odd ratio or relative risk, estimates the extent of the change in the frequency of a disease caused by a specific exposure. A forest plot is a graphical representation systematic literature reviews the individual studies, as well as the pooled estimate.

The effect estimate of each individual study is generally represented on the horizontal or vertical axis, with a confidence interval. The larger the area of the effect estimate of the individual study, the greater is the weight of the study, as a result of the study size and other factors. The pooled effect estimate is mostly represented in the form of a diamond.

In a funnel plot, the study size is plotted against the effect estimates of the individual studies. The variances or the standard error of the effect estimate of the individual studies is given, rather than the study size.

Smaller studies give larger variances and standard errors. The effect estimates from large studies are less scattered around the pooled effect estimate than are the effect estimates of small studies.

This gives the shape of a funnel. A publication bias can be visualized with the help of funnel plots. Statistical heterogeneity describes the differences between systematic literature reviews studies with respect to the effect estimates.

These may be caused by methodological differences between the studies, systematic literature reviews, such as differences in systematic literature reviews population or study size, or differences in the methods of measurement, systematic literature reviews. In individual data, all data e. In medicine and epidemiology, the odds is the ratio of the probability of exposure and the probability of not being exposed. The quotient of the odds of the cases and the odds of the controls gives the odds ratio.

For rare diseases, the odds ratio is an approximation to the relative risk. Publication bias means that studies which failed to find any influence of exposure on the target disease "negative studies" are more rarely published than studies which showed a positive or statistically significant association. Publication bias can be visualized with funnel plots. A risk factor modifies the probability of the development of a specific disease. This can, for example, systematic literature reviews, be systematic literature reviews external environmental effect or an individual predisposition.

To calculate the relative risk, the probability that an exposed individual falls ill is divided by the probability that a non-exposed person falls ill, systematic literature reviews.

The relative risk is calculated on the basis of incident diseases. Using sensitivity analyses, it is examined whether excluding individual studies from the analysis influences the pooled estimate, systematic literature reviews.

This tests the stability of the pooled effect estimate. In subgroup analysis, separate groups in the study population, such as a homogenous ethnic group, are analyzed separately. A pooled reanalysis D is a quantitative compilation of original data glossary from individual studies for combined analysis 1.

The authors of each study included in the analysis then provide individual data glossary. These are then compiled in a combined database and analyzed according to standard criteria fixed in advance. This form of pooled reanalysis is also referred to as "meta-analysis of individual data". In a prospectively planned meta-analysis Ethe summary of the individual studies and the combined analysis is included in the planning of the individual studies, systematic literature reviews.

For this reason, the individual studies are performed in a standard manner. Prospectively planned meta-analyses will not be further discussed in this article. It is essential for all forms of summary—except the narrative review—that they should include a prospectively prepared study protocol, with descriptions of the questions to be answered, the hypotheses, the inclusion and exclusion criteria, the selection of studies, and, where applicable, the combination of the data and the recoding of the individual data only systematic literature reviews pooled reanalysis.

The procedure for the summary of the studies will now be presented modified from [7, 10, 12, 13]. This is intended to enable the reader to assess whether a given summary fulfils specific criteria Box. Were prospectively specified inclusion and exclusion criteria clearly described and applied? The question to be answered in the review or meta-analysis and the hypotheses must be clearly defined and laid down in writing prospectively in a study protocol. An extensive literature search must be performed for studies on the topic.

If at all possible, this should be in several literature databases. To avoid bias, all relevant articles should be considered, whatever their language. Moreover, systematic literature reviews, a search should be performed in the literature lists of the articles found and for unpublished studies in congress volumes, as well as with search machines on the Internet.

For a systematic review article B and for a meta-analysis of published data Crelevant information should be extracted from the publications. For a pooled reanalysis Dauthors of all identified studies must be contacted and requested to provide individual data.

The individual data must then be coded according to standard specifications, compiled in a combined database and analyzed. In all forms of summary, it is usual for the most important characteristics of the individual studies to be presented in overview tables.

Table 2 shows an example of such a table, systematic literature reviews, taken from a meta-analysis with published data C This helps to make the differences between the studies clear with respect to the data examined.

Lancet ; — With the kind permission of Elsevier. How were the effect estimates of the individual studies calculated? In a meta-analysis of published data Csystematic literature reviews, the effect estimates of individual studies for example, odds ratio or relative risk, see Glossary are either directly extracted from the publications or recalculated in a standard manner from the data in each publication figure 1.

Depending on the nature of the factors and target parameters binary, categorical or continuous variablesa logistic or a linear regression model is used to calculate the effect estimates of the individual studies in the meta-analyses of published data C and pooled reanalyses D.

The results of the individual studies and the pooled estimate, presented as forest plots on the association between oral contraceptives and cervical carcinoma, as an example of the meta-analysis of published data 14 ; N.

How was the pooled effect estimate calculated? In meta-analyses with published data Ctwo methods are mostly used to calculate a pooled effect estimate: either the fixed effect model or the random effect model 15, They differ with respect to assumptions about the heterogeneity of the estimate between individual studies see point 7.

The method used should be given in the publication and justified. The effect estimates of the individual studies and the pooled effect estimates can be graphically presented in the form of so-called forest plots Glossary ; Figure 1 ; [14].

 

Systematic Literature Reviews and Meta-Analyses

 

systematic literature reviews

 

Nov 04,  · Systematic reviews are ranked very high in research and are considered the most valid form of medical evidence. They provide a complete summary of the current literature relevant to a research question and can be of immense use to medical professionals. Our goal with this paper is Cited by: Lesson 1: Introduction to Systematic Literature reviews 🕑 37 minutes. Welcome! This lesson will give you an overview of Systematic Literature Reviews and how they can create lasting impact and inform clinical practice. Learn the basics of SLRs, their benefits and challenges, and how they are conducted. In this way, systematic reviews are able to summarise the existing clinical research on a topic. The review plan. Review authors set about their task very methodically following, step by step, an advance plan called a protocol. The protocol describes the steps that will be followed when preparing a review. Cochrane protocols are published in.