What Is a Systematic Review?

When you need to answer a distinctly formulated research question and inform about the methods you have used to obtain the answer, you write a systematic review. It is completed with the help of recurrent methods used for finding, collecting, and synthesizing the evidence on the question.

What Stands Behind a Systematic Review?

This review is a summary of the research work that has already been done on your research question. A systematic type differs from other reviews by its research methods used to eliminate bias. These methods are repeated, making the overall approach systematic and formal. When you create such a review, you:

• make up a research question
• choose the type of protocol and develop it
• look for all the studies that are relevant to your research question
• utilize the specific selection criteria
• extract the important data
• synthesize this data
• write a report and publish it in a reputable academic media

While creating a systematic review, you can use the guidelines like the Cochrane Handbook for Systematic Reviews and others that are available online. The guidelines will get you across the most vital step of the writing process.

Systematic reviews are common for most medical and public health research as well as in other fields of study like social science. You answer the research question by synthesis all evidence that relates to it and assessing its quality. When you synthesize the found evidence, you compile different information to obtain a cohesive story. You can use qualitative (narrative), quantitative, or both types of synthesis.

Comparison of Systematic Reviews and Meta-Analysis

A meta-analysis is often confused with a systematic review. However, it is not a review at all. It is a statistical analysis and technique used in systematic and other types of reviews to synthesize the results found in two or more existing studies. A meta-analysis is usually helpful in assessing the size of the effects.

Why Are Systematic and Literature Reviews Different?

Literature reviews do not use such formal approaches as systematic ones. The researcher of the topic does not use any formal or explicit methods. They only qualitatively describe, summarize, and evaluate the previous results. Literature reviews are not too time-consuming. Though they are also consistent and insightful, there is a high risk of bias and lower transparency.

Difference Between Systematic and Scoping Reviews

A scoping review is quite similar to a systematic one. It is meant to reduce bias, and it uses repeatable and transparent methods and techniques. However, a scoping review is a different review type. Its goal is the essential difference. It does not answer a research question but explores a whole topic. The researcher’s aim here is to define the main concepts, evidence, and supporting theories related to the subject. The gap identification in the current research design is also a part of the goal. You can use a scoping review as an exploratory part that prepares for a systematic review. Though it can also be a separate project depending on the goals.

When Are Systematic Reviews Appropriate?

The most appropriate use of a systematic review is when you want to demonstrate the efficacy of medical treatment. You need to consider the following to reach the review’s goals:

1. You need a correctly formulated question about the effectiveness of the treatment intervention. This question should have been previously researched by many explorers. If there is no previous work done on the subject, you won’t have anything to review.
2. It is important to have a research team consisting of at least three people. Three researchers are important for the smooth flow of the process. You can also have an advisory team of six or more people. However, if you are a student and doing your review on your own for an academic paper or another assignment, having advisors may be problematic. So, you need to consider other ways of ensuring the reliability and validity of your review.
3. Think about getting access to scientific databases and academic journal archives. Your institution can provide such access if you ask them to do that.
4. Getting enough time and meeting deadlines are important things to consider. Systematic reviews are rather time-consuming. Their authors may spend up to six months full-time working on them. If it is your academic assignment, your time may be confined by the deadline. So, you have to narrow down the scope of your review to meet the schedule requirements.
5. You need brand-new software for bibliographic, statistical, word-processing, and spreadsheeting purposes. You can use Microsoft Word, SPSS, Excel, or EndNote within the research process.

Benefits and Drawbacks of Systematic Reviews

Like other types of academic reviews, a systematic review has its benefits and drawbacks. The main advantages are the following:

✔️ This review can minimize the risks of research bias because you can take all the available evidence into account and assess it for potential bias.	❌ The systematic reviews are time-consuming.
✔️ The transparency of all the methods applied to this review does not allow any third parties to distort the results and scrutinize the conclusions.	❌ The scope of such reviews is too narrow because the review can answer only one research question and cannot cover the entire scope of the problems on the topic.
✔️ Such reviews can be complemented and updated by other researchers.

How to Do a Systematic Review Step-by-Step?

You can use these seven steps to create a professional systematic review as a basis for your work plan and schedule. Following an accurate plan is especially important when you are short of time.

Step 1. Research Question Formulation

This first step is the most important one. The research should help you:

• ✔️ consistently communicate your research goals to practitioners and members of your team;
• ✔️ make decisions related to planning and course of your systematic review creation.

You also need to check how accurate your research question is. It needs four components united by the acronym PICO:

1. Problems or populations
2. Interventions
3. Comparisons
4. Outcomes

You can check the effectiveness of these four components by rearranging them like “How effective is I versus C for getting O in P?” You can also insert the fifth component in this scheme. It is a type of design, and it will change the acronym into PICOT.

Step 2. Protocol Development

Your systematic review needs a research plan that is known as a protocol. If you have an accurate plan, you and your team will work more efficiently, and the chances to reduce bias will increase.

The protocol has to consist of the following items:

• information about the background and context of the research question: don’t forget to emphasize why it is essential;
• objectives of the research project: your rephrased research question can be such an objective;
• the methods you are going to use based on the selection criteria (which studies should be included and excluded from your review and why), search strategies (discuss with your team), and analysis (what kind of information to collect and how to synthesize it).

If you are a professional researcher and want your review published, involve an advisory committee. It has to consist of at least six individuals with experience in the topic. They can advise you on making decisions about the protocol. The protocol, in this case, should be registered by submitting it to one of the widely used databases like ClinicalTrials.gov or PROSPERO.

For example, Fabian and colleagues registered their protocol in PROSPERO in 2012 and then published it. It included the review background, objectives of the research, and the methods they were planning to utilize.

Step 3. Finding All Relevant Studies

This step is the most time-consuming, though the most responsible one. You need to be very careful while picking up previous studies to reduce bias. Of course, the scope of sources will depend on your field of study and research question. Though, you need to consider these four categories:

1. Databases for finding peer-reviewed works. You can use Scopus or PubMed if it is about medical research. Be careful about the terms you will be using for your search and include word synonyms if needed. You can also utilize Boolean operators if the search seems ineffective.
2. Hand searching by scanning appropriate conference minutes and proceedings or scanning reference lists.
3. Gray literature, including documentaries from governmental and non-governmental institutions, academic establishments, and graduate student theses. You can look for them in the NDLTD (the Networked Digital Library of Theses and Dissertations). Clinical trial reports are also a part of the gray literature in medicine.
4. Experts’ advice related to your field, including their unpublished projects.

You do not have to look through all the sources found at this stage. You can only store the relevant citations with the help of citation generators online.

For example, Fabian and colleagues indicated their use of the following resources:

• databases: Scopus, LILACS, and EMBASE;
• hand search: reference lists of the related scientific research and journal articles;
• gray literature from the MetaRegister of Controlled Trials;
• nutritionist experts’ unpublished works on healthy diets and vegetarianism.

Step 4. The Application of the Data Collection Criteria

It is better if you do this job in a group of three people. Two researchers can read the sources and select those they find appropriate for the review. They have to follow the selection criteria defined by the protocol. The third researcher can be involved in the final resolutions about the appropriateness of choice and solving the issues if there are contradictions between the first two researchers. This inter-rater should understand the selection criteria well before the start of work.

If you are a student and have a task to write a systematic review, you may not have such a team of three. So, you need to be very accurate about developing and applying the selection criteria. You can even indicate the fact that you were working alone in the list of limitations in the discussion section of your review.

There are two phases of the selection criteria application:

1. You can read the titles and abstracts first and decide whether the work meets the criteria. If they don’t exclude them from the list.
2. Then, you read the whole text and download the works that should be included in the project remaining from the first phase. You may even encounter articles that are not available in any library, so you can contact the author and ask them to send you a copy of it. Now, you need to decide whether the works meet your data collection criteria right now.

Don’t forget to keep a detailed record of all the sources that you have excluded and included in your project. You can you a PRISMA flow diagram at the end of the selection process to summarize your findings.

Step 5. Data Extraction

So, you need to extract the information from the selected studies now. You need to collect the following systematic information from these works:

• The information related to the methods used and the results of the study. It will depend on your research question, but it is useful when it contains the study design, year, context, sizes of samples, findings, and conclusions. You may contact the author if you feel that you need some concrete information but it is missing.
• Your considerations about the quality of the information and outcomes, as well as about the possible bias.

You can use specific forms to collect this information. You can find the templates in The Registry of Methods and Tools for Evidence-Informed Decision-Making and other reputable databases.

You also need to extract this data in a team of three. Two researchers will work on their own, and the third will solve any disagreement issues.

Step 6. Data Synthesizing

This step is about putting together all the information that has been collected. It should be compiled in a consistent and cohesive story. You can use the following approaches to this stage:

• Narrative or qualitative one to sum up all the data in words. At the end of the story, you will have to evaluate the overall quality of the evidence collected.
• A quantitative approach for using statistical techniques, to sum up and compare the different study results. A meta-analysis is the most suitable approach here. You will be able to put together the outcomes of different studies and formulate the overall result.

In general, you can even combine these two approaches when you see that you need such a combination. If you see that some data from different studies cannot be compared, you can use a narrative variant. Though, you need to explain why a quantitative approach cannot be used.

Step 7. Report Writing and Publishing

The main goal of a systematic review is to write a consistent article that can share the answers to your research question and provide data-based explanations of how you have arrived at such conclusions.

The article usually consists of the following parts (sections):

• Abstract - the review summary
• Introduction - indicating the rationale of the research project and objectives
• Methods - what selection criteria, search designs, data extraction methods, and ways of data synthesis have you used
• Results - selection process outcomes, characteristics of the study, bias risks, and the overall synthesis results
• Discussion - results’ interpretation and review limitations
• Conclusion - you indicate the answer to the research question and its practical implications for further research projects

Use the PRISMA checklist to ensure that you have included everything needed in your systematic review. Publish your report in a systematic review database or an academic peer-reviewed journal.

Final Thoughts

A systematic review is a great way to consider all the initial sources and previous studies on the research question of your project. The research results will look more reputable, reliable, and valid if they are based on consistent and well-researched evidence.

You can see here how to create a systematic review and what benefits it can provide. If you follow the principles and recommendations provided in this article, your research project is sure to be a success.