Systematic reviews are performed for synthesizing the evidence of multiple scientific investigations to answer a specific research question in a manner that is reproducible and transparent while seeking to include all published evidence on the topic followed evaluating the quality of this evidence. A Systematic review remains among the best forms of evidence and reduces the bias inherent in other methods. In the disciplines of public policy health and health sciences, systematic reviews have become the main methodology. Previously, some have provided that structure research ought to embrace the systematic review, but limited guidance is available. This section presented an overview of the various steps involved in performing a systematic review. This information should provide proper guidance for those who are conducting a systematic literature review (Davis, 2019 ).

Key characteristics of the systematic review

• Identification
  of a research question
• Inclusion
  & exclusion criteria
• Rigorous
  & systematic search of the literature
• Critical appraisal of included studies
• Data extraction and management
• Analysis & interpretation of
  results
• Report for publication

Different types of the systematic review

The systematic review mainly classified into three types, including (1) meta-analysis, (2) quantitative analysis and (3) qualitative analysis.

Meta-analysis: A meta-analysis utilizes statistical methods to incorporate appraisals of impact from relevant studies that are independent yet comparable and outline them.

Quantitative: To combine the results of 2 or more studies by using statistical analysis is called quantitative analysis.

Qualitative: The qualitative analysis generally defined as the results of the relevant studies are summarized but not combined statistically.

Steps to be followed before drafting a systematic review

Identification of a research question

The identification of the research question is significant before undertaking a systematic review of literature. For instance, for what reason is this survey essential? What question should be replying?. There are a variety of frameworks/tools available for supporting this process such as SPIDER, PICOS/PICO, SPICE and PEO criteria. These kinds of frameworks help to break down the question into relevant subcomponents and map them to concepts, to derive a formalized search criterion. This step is essential for finding literature relevant to the subject (Jahan et al., 2016 ).

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Inclusion & exclusion criteria

It is important to determine the eligibility criteria before starting the systematic review, including methods, study design, set criteria for the topic and the methodological quality of studies.

Guidelines for systematic review

Researchers widely follow the PRISMA guidelines in writing a systematic review. The PRISMA guidelines guide researchers on how to write a systematic review and that comprises a flow diagram and a 27-item checklist. A protocol of PRISMA guidelines including (1) Databases to be searched and additional sources (2) Keywords to be used in the search strategy (3) Limits applied to the search (4) Limits enforced to the search (5) Screening process (6) Data to be extracted and (7) Summary of data to be reported.

Screening of the articles

Some vital web source for the article screening including PubMed (Biomedical and life sciences topic), Medline (Biomedical information and life sciences), Embase (Biomedical information), Web of Science (Multidiscipline science), Biosis (Life sciences and biomedical topics), PsycINFO (Behaviour and mental health), SCOPUS (Life sciences, social sciences, physical sciences and health science), CINAHL (Cumulative Index to Nursing and Allied Health Literature), Cochrane Library (Database of systematic reviews), CENTRAL (The Cochrane Central Register of Controlled Trials) and OpenGrey (Grey literature).

 Title and abstract screening: Initially, the title and abstract of the articles should be screened whether the title and abstract are relevant to the present research.

Full-text review: The remaining articles screened in a way mentioned above and the relevant sections are in their entire texts.

Data extraction: The essential data of the articles are extracted in a data extract sheet in a uniform and structured manner. The extraction sheets may differ based on the study’s purpose. Generally, the data extraction sheet containing the title of the article, study design, region, sample size, interventions and outcomes (Mueller et al., 2017 ).

Data analysis

The screened studies results can be analyzed by separating them based on the subthemes; themes often referred to as meta-synthesis (Siddaway et al., 2019 ).

The systematic review should be in the following structure

Abstract

The abstract should contain a brief background, the aim of the study, a summary of the methodology, an overview of the results, conclusion and keywords.

Introduction

The chapter contains a brief background of the present study, followed by an overview of the aim and objectives of the research undertaken.

Methods

The methodology should be containing a full justification and explanation for the managing and searching steps. Specifically, the justification includes a thorough explanation about inclusion/exclusion criteria, search string, searching strategy, limitations, how studies were screened, data extraction protocol, method of quality assessment and statistical analysis.

Results

The quantitative explanation and evidence must be given to the process of study exclusion/inclusion and summarized in a specific flow diagram. A characteristic of the study summary should be obtained, the sum of all studies, age range, mean/median and other characteristics.

Discussion

To discuss the present study with the light of relevant research done in other studies. The main component of the discussion chapter should be focused on discussing and identifying the limitations of the studies included in the review.

Conclusion

The conclusion should be containing the summary of different aspects of the present study, and the results generated as well as the future scope of research and the findings derived from the present study.

Performing a systematic review of literature is quite complicated and time-consuming process which takes between 6 and 18 months on average depends on the study design. The guidelines mentioned above provide a good outline for conducting a systematic review of the literature. This framework especially is essential for early career researchers and medical students to enhance their writing knowledge on the systematic review of the literature.

Quick reference Table

Key points:

• A systematic review of the literature tends to be one of the most trusted sources of
  high-quality information for clinical decisions.

• Knowing the elements
  of a review will help practitioners evaluate their output more effectively.

• Many formal structures
  help organize and monitor evaluations, for which reproducibility is
  recommended.