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Using the PRISMA Diagram in Literature Reviews for Medical Devices

PRISMA DIAGRAM - Literature Review Software

As for any type of research, the value of a systematic review is determined by its quality, encompassing both the methodology employed and the manner in which the results are reported. 1  

In 1999, an international group published the QUOROM (QUality Of Reporting Of Meta-analyses) Statement to address suboptimal reporting of meta-analyses at that time. 2 

In 2009, the guideline was updated to include systematic reviews and was renamed PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses).1 The PRISMA 2020 statement replaces the 2009 statement and includes new reporting guidance that reflects advances in methods to identify, select, appraise, and synthesize studies. The structure and presentation of the items have been modified to facilitate implementation. 3 

PRISMA is an evidence-based minimum set of items for reporting in systematic reviews and meta-analyses. PRISMA primarily focuses on the reporting of reviews evaluating the effects of interventions, but can also be used as a basis for reporting systematic reviews with objectives other than evaluating interventions (e.g. evaluating aetiology, prevalence, diagnosis or prognosis).3 

The PRISMA Statement consists of a 27-item checklist and a 4-phase flow diagram, designed to ensure transparency and completeness in reporting these types of studies in scientific publications. The checklist addresses important components within each section of the systematic review, including the title, abstract, methods, results, discussion, and funding. An extended checklist is also available on the PRISMA website 

The PRISMA diagram is a graphical representation of the flow of information through the different phases of systematic review. It maps the number of articles identified, screened, found eligible, and finally included, including the reasons for exclusion. 

In this blog post, we will focus on the use of the PRISMA diagram, as the PRISMA checklist is specifically tailored towards reporting of systematic literature reviews and meta-analyses for publication and contains a number of items that are not related to the process of conducting a systematic literature review itself. 

Why use the PRISMA diagram?

While using the PRISMA diagram is not mandatory for all systematic literature reviews, its guidelines can serve as valuable guidance for researchers aiming to conduct high-quality, transparent, and reproducible reviews of the literature. Using a PRISMA flow chart however is recommended for several reasons: 

  • Transparency: It provides a clear and transparent depiction of the entire systematic review or meta-analysis process, from initial identification of records through to final inclusion of studies. This transparency helps readers understand the selection process and any potential biases. 
  • Reproducibility: By following PRISMA guidelines and creating a flow chart, you make your review or meta-analysis more reproducible. Others can understand and replicate your methods more easily, which enhances the credibility of your work. 
  • Identification of Bias: The flow chart allows you to identify and document any potential sources of bias in the selection process. For example, if many studies were excluded at a certain stage, you can investigate whether there was a systematic reason for this, which could indicate bias. 
  • Quality Assurance: Creating a PRISMA flow chart ensures that you have followed a standardized approach to reporting your review or meta-analysis. This helps to maintain the quality and consistency of reporting across different studies. 
  • Publication Requirement: Many journals require authors to adhere to PRISMA guidelines and provide a flow chart as part of the manuscript submission process. By using a PRISMA flow chart, you ensure that your manuscript meets the requirements of these journals, increasing the likelihood of publication. 

How to create a PRISMA Diagram

While the outline of the PRISMA diagram is downloadable from the PRISMA Statement website, there are a number of free online tools available that help you to create a compliant PRISMA diagram, such as this Shinyapp.4

Sources of Information

PRISMA diagram

Let’s first have a look at the different sources of information that are applicable in the full version of the PRISMA diagram:

  • Previous studies: The left column “previous studies” takes the summary of the PRISMA diagram of your earlier review(s), to add to the total of included studies at the bottom.  
  • New studies from database or registers: The middle part summarizes all results from databases (e.g. PubMed, Embase, Web of Science) and registers, such as clinical trial registers or domain-specific registries. These are studies that were found through structured search strategies applied to relevant databases and registers. 
  • New studies via other methods: The right part of the PRISMA diagram lists results from methods other than searching databases and registers. This could include studies found through manual searching of journals, conference proceedings, or other non-database sources, such as websites of professional organizations that are often used to look for clinical guidelines when searching for the state-of-the-art.  

 

Please note that search engines such as Google Scholar can either be reported in the middle section or the right section. Discussions are ongoing whether or not Google Scholar should be handled as a database or not. Regardless of where you choose to include the Google Scholar results in your PRISMA diagram, it is advisable to provide proper justification for that choice in your report. 

Stepwise approach

1. Identification

The flow diagram starts with the initial number of records identified through various sources such as literature databases, manual searches, or other means.  

PRISMA: Identification

While focusing on the middle section, you should add the total number of combined results from all databases (including duplicates) after the equal sign where it says Databases (n=). Many researchers also add notations in the box for the number of results from each database search, for example, PubMed (n=335), Embase (n= 600), and so on.  If you search trial registers, such as ClinicalTrials.gov,  you should enter that number after the equal sign inRegisters (n=). 

2. Deduplication

To avoid reviewing duplicate articles, you need to remove any articles that appear more than once in your results. Enter the number of records removed as duplicates in the second box on your PRISMA template. If you are using automation tools to help evaluate the relevance of citations in your results, you would also enter that number here.

PRISMA Deduplication

It is important to mention that the PRISMA 2020 flow chart did not include the step to deduplicate articles from other sources in the main flow as per the flowchart. In practice deduplication has to be done for these as well. 

3. Screening

This stage involves screening the titles and abstracts of the identified records to assess their relevance to the research question or objective

PRISMA Screening

Any articles that appear to help you provide an answer to your research question should be included. Record the number of articles excluded through title/abstract screening.  Subtract the number of excluded records from the total number screened and this will be your number sought for retrieval (see next step)For MDR literature reviews, you need to add exclusion reasons at this level, while it is optional for other literature reviews. Please refer to IMDRF version of the PRISMA flowchart and MDCG 202-13.  

4. Full-Text retrieval

In the next step, full-text articles of potentially relevant studies are assessed against predetermined eligibility criteria. 

PRISMA: Full-text retrieval

To do so, you will first need to find the get your hands on the full text articles. Many of the articles you have selected will be freely available online through the links in your database such as PubMed, or available via websites such as Unpaywall. Others will be available through purchase. 

Nevertheless, there will be articles that will be unavailable. List the number of articles for which you are unable to find the full text. Please note that the unavailability of full text as such is generally not accepted by notified bodies, unless you have documentation that you went through some lengths to try and obtain the full text, e.g. by contacting the corresponding author of the publication. 

5. Full-Text Review

After reviewing all articles in the full-text screening stage for eligibility, enter the total number of articles you exclude in the box titled “Reports excluded,” and then list your reasons for excluding the articles as well as the number of records excluded for each reason.

PRISMA: Full Text Review

Examples include wrong setting, wrong patient population, wrong intervention, wrong dosage, etc. You should only count an excluded article once in your list even if it meets multiple exclusion criteria. 

6. Summary

The final step is to subtract the number of records excluded during the eligibility review of full texts from the total number of articles reviewed for eligibility, combining numbers from your literature search results from other sources and previous versions, if applicable.   

PRISMA -Summary

You have now completed your PRISMA flow diagram (unless you have also performed searches in non-database sources).

Alternatives for the PRISMA diagram

While PRISMA is highly recommended and standardized for systematic literature reviews, there are alternative ways to report an overview of the results of a systematic literature review, depending on the specific objectives, methodology, and preferences of the researchers. Some alternatives to the PRISMA diagram include: 

  • Flowcharts: Similar to a PRISMA diagram, flowcharts can visually represent the flow of information through the different stages of the review process. Flowcharts can be customized to fit the specific requirements of the review and can include additional details or steps as needed. 
  • Tree diagrams: Tree diagrams, also known as dendrograms, can illustrate hierarchical relationships between different categories or classifications of studies in literature. These diagrams can help organize and visualize complex information in a structured manner. 
  • Tabular format: Tables can be used to present detailed information about study selection criteria, characteristics of included studies, and reasons for exclusion. They offer a structured format for organizing data and can be customized to include relevant information. 
  • Textual Summary: A well-written textual summary can effectively communicate the review process, including search strategies, screening methods, and reasons for study inclusion/exclusion. This approach may be particularly useful for reviews with fewer included studies or for supplementary information alongside other visual representations. 

Conclusion

The PRISMA statement is applicable to any systematic review or meta-analysis, regardless of the topic or discipline. It is widely recognized and endorsed by numerous journals and organizations within the scientific community. 

Adhering to the PRISMA guidelines enhances the credibility and reproducibility of systematic reviews and meta-analyses. Transparent reporting facilitates critical appraisal of the study methods and findings, ultimately contributing to evidence-based decision-making in healthcare and other fields. 

Please note that the PRISMA statement is periodically updated to reflect advances in methodology and reporting standards. Researchers should consult the latest version of the PRISMA statement when preparing their literature reviews. 

References and reading

  1. Moher D, Liberati A, Tetzlaff J, et al. Preferred reporting items for systematic reviews and meta-analyses: The PRISMA statement. PLoS Med. 2009;6(7). doi:10.1371/journal.pmed.1000097
  2. Moher D, Cook DJ, Eastwood S, Olkin I, Rennie D, Stroup DF. Improving the quality of reports of meta-analyses of randomised controlled trials: the QUOROM statement. Quality of Reporting of Meta-analyses. Lancet (London, England). 1999;354(9193):1896-1900. doi:10.1016/s0140-6736(99)04149-5
  3. Page MJ, McKenzie JE, Bossuyt PM, et al. The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ. 2021;372. doi:10.1136/bmj.n71
  4. Haddaway NR, Page MJ, Pritchard CC, McGuinness LA. PRISMA2020 : An R package and Shiny app for producing PRISMA 2020‐compliant flow diagrams, with interactivity for optimised digital transparency and Open Synthesis. Campbell Syst Rev. 2022;18(2):e1230. doi:10.1002/cl2.1230

 

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