Published on June 15, 2022 by Shaun Turney. Revised on September 14, 2022. A systematic review is a type of review that uses repeatable methods
to find, select, and synthesize all available evidence. It answers a clearly formulated research question and explicitly states the methods used to arrive at the answer. They answered the question “What is the effectiveness of probiotics in reducing eczema symptoms and improving quality of life in patients with eczema?” In this context, a probiotic is a health product that contains live
microorganisms and is taken by mouth. Eczema is a common skin condition that causes red, itchy skin. They used systematic methods to find, select, and synthesize all available evidence, and they described these methods in detail in their article. Based on the evidence, Boyle and colleagues concluded that probiotics cannot be recommended for reducing eczema symptoms or improving quality of life in patients with eczema. A review is an overview of the research that’s already been completed on a topic. What makes a systematic review different from other types of reviews is that the research methods are designed to reduce bias. The methods are repeatable, and the approach is formal and systematic: Although multiple sets of guidelines exist, the Cochrane Handbook for Systematic Reviews is among the most widely used. It provides detailed guidelines on how to complete each step of the systematic review process. Systematic
reviews are most commonly used in medical and public health research, but they can also be found in other disciplines. Systematic reviews typically answer their research question by synthesizing all available evidence and evaluating the quality of the evidence. Synthesizing means bringing together different information to tell a single, cohesive story. The synthesis can be narrative
(qualitative), quantitative, or both. Systematic reviews often quantitatively synthesize the evidence using a meta-analysis. A meta-analysis is a statistical analysis, not a type of review. A meta-analysis is a technique to synthesize results
from multiple studies. It’s a statistical analysis that combines the results of two or more studies, usually to estimate an effect size. Scribbr editors not only correct grammar and spelling mistakes, but also strengthen your writing by making sure your paper is free of vague language, redundant words and awkward
phrasing. See editing example Systematic review vs. literature reviewA literature review is a type of review that uses a less systematic and formal approach than a systematic review. Typically, an expert in a topic will qualitatively summarize and evaluate previous work, without using a formal, explicit method. Although literature reviews are often less time-consuming and can be insightful or helpful, they have a higher risk of bias and are less transparent than systematic reviews. Systematic review vs. scoping reviewSimilar to a systematic review, a scoping review is a type of review that tries to minimize bias by using transparent and repeatable methods. However, a scoping review isn’t a type of systematic review. The most important difference is the goal: rather than answering a specific question, a scoping review explores a topic. The researcher tries to identify the main concepts, theories, and evidence, as well as gaps in the current research. Sometimes scoping reviews are an exploratory preparation step for a systematic review, and sometimes they are a standalone project. When to conduct a systematic reviewA systematic review is a good choice of review if you want to answer a question about the effectiveness of an intervention, such as a medical treatment. To conduct a systematic review, you’ll need the following:
Pros and cons of systematic reviewsA systematic review has many pros.
Systematic reviews also have a few cons.
Step-by-step example of a systematic reviewThe 7 steps for conducting a systematic review are explained with an example. Step 1: Formulate a research questionFormulating the research question is probably the most important step of a systematic review. A clear research question will:
A good research question for a systematic review has four components, which you can remember with the acronym PICO:
You can rearrange these four components to write your research question:
Sometimes, you may want to include a fifth component, the type of study design. In this case, the acronym is PICOT.
Their research question was:
Step 2: Develop a protocolA protocol is a document that contains your research plan for the systematic review. This is an important step because having a plan allows you to work more efficiently and reduces bias. Your protocol should include the following components:
If you’re a professional seeking to publish your review, it’s a good idea to bring together an advisory committee. This is a group of about six people who have experience in the topic you’re researching. They can help you make decisions about your protocol. It’s highly recommended to register your protocol. Registering your protocol means submitting it to a database such as PROSPERO or ClinicalTrials.gov. Example: Develop a protocolIn 2006, Boyle and colleagues published a protocol that included background information, a research objective, and proposed methods.Step 3: Search for all relevant studiesSearching for relevant studies is the most time-consuming step of a systematic review. To reduce bias, it’s important to search for relevant studies very thoroughly. Your strategy will depend on your field and your research question, but sources generally fall into these four categories:
At this stage of your review, you won’t read the articles yet. Simply save any potentially relevant citations using bibliographic software, such as Scribbr’s APA or MLA Generator. Example: Search for all relevant studiesBoyle and colleagues searched the following sources for relevant studies:
Step 4: Apply the selection criteriaApplying the selection criteria is a three-person job. Two of you will independently read the studies and decide which to include in your review based on the selection criteria you established in your protocol. The third person’s job is to break any ties. To increase inter-rater reliability, ensure that everyone thoroughly understands the selection criteria before you begin. If you’re writing a systematic review as a student for an assignment, you might not have a team. In this case, you’ll have to apply the selection criteria on your own; you can mention this as a limitation in your paper’s discussion. You should apply the selection criteria in two phases:
It’s very important to keep a meticulous record of why you included or excluded each article. When the selection process is complete, you can summarize what you did using a PRISMA flow diagram. Example: Apply the selection criteriaBoyle and Tang independently read the titles and abstracts of the studies that were identified during their search. They excluded any study that didn’t refer to a randomized control trial of probiotics for eczema.Next, Boyle and colleagues found the full texts for each of the remaining studies. Boyle and Tang read through the articles to decide if any more studies needed to be excluded based on the selection criteria. When Boyle and Tang disagreed about whether a study should be excluded, they discussed it with Varigos until the three researchers came to an agreement. After applying the selection criteria, they were left with 12 studies involving 781 participants. Step 5: Extract the dataExtracting the data means collecting information from the selected studies in a systematic way. There are two types of information you need to collect from each study:
You should collect this information using forms. You can find sample forms in The Registry of Methods and Tools for Evidence-Informed Decision Making and the Grading of Recommendations, Assessment, Development and Evaluations Working Group. Extracting the data is also a three-person job. Two people should do this step independently, and the third person will resolve any disagreements. Example: Extract the dataBoyle and Tang independently extracted the data using data collection forms. They collected data about the studies’ populations, methods, and outcomes.They also collected data about possible sources of bias, such as how the study participants were randomized into the control and treatment groups. If Boyle and Tang disagreed on anything, then Varigos broke the tie. Boyle and Bath-Hextall entered the data from the forms into a computer spreadsheet. Step 6: Synthesize the dataSynthesizing the data means bringing together the information you collected into a single, cohesive story. There are two main approaches to synthesizing the data:
Generally, you should use both approaches together whenever possible. If you don’t have enough data, or the data from different studies aren’t comparable, then you can take just a narrative approach. However, you should justify why a quantitative approach wasn’t possible. Example: Synthesize the dataBoyle and colleagues used a meta-analysis approach to synthesize the data. They combined data from different studies to calculate overall effect sizes (risk ratios and differences between means) for the outcomes. They calculated confidence intervals for these effect sizes.Boyle and colleagues also divided the studies into subgroups, such as studies about babies, children, and adults, and analyzed the effect sizes within each group. Boyle and colleagues’ meta-analysis found that there was no significant effect of probiotic treatment on eczema symptoms, either overall or in any subgroup. Step 7: Write and publish a reportThe purpose of writing a systematic review article is to share the answer to your research question and explain how you arrived at this answer. Your article should include the following sections:
To verify that your report includes everything it needs, you can use the PRISMA checklist. Once your report is written, you can publish it in a systematic review database, such as the Cochrane Database of Systematic Reviews, and/or in a peer-reviewed journal. Example: Write and publish a reportBoyle and colleagues published their report in 2008. They published it in the Cochrane Database of Systematic Reviews and a peer-reviewed journal called Clinical and Experimental Allergy. They updated their report in 2018.In their report, Boyle and colleagues concluded that probiotics cannot be recommended for reducing eczema symptoms or improving quality of life in patients with eczema. Frequently asked questions about systematic reviewsIs this article helpful?You have already voted. Thanks :-) Your vote is saved :-) Processing your vote... What are systematic reviews in research?Systematic reviews aim to identify, evaluate, and summarize the findings of all relevant individual studies over a health-related issue, thereby making the available evidence more accessible to decision makers.
What is a metaA 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.
What is review and metaWhat is a systematic review or meta-analysis? A systematic review answers a defined research question by collecting and summarising all empirical evidence that fits pre-specified eligibility criteria. A meta-analysis is the use of statistical methods to summarise the results of these studies.
What is the purpose of systematic review?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).
|