Understanding the Importance of PRISMA in Systematic Reviews: A Deep Dive into Flow Diagram

PRISMA Stands for Preferred Reporting Items for Systematic Reviews and Meta-Analysis. The main aim of PRISMA is to help authors improve the reporting of systematic reviews and meta-analyses. It is an evidence-based minimum set of items for reporting in systematic reviews and meta-analyses. Systematic Reviews and Meta-Analyses are important tools for summarizing evidence accurately and reliably. They have multiple benefits. They help professionals stay up to date, give substantial proof to policymakers to assess the risks, provide a logical ground for guideline creators, and help editors to judge the merits of publishing reports of fresh studies and many more.
Evolution of PRISMA
There is a lot of evidence that systematic reviews could not report key information. This actually diminished the usefulness of systematic reviews. The relevance and importance of systematic reviews are maintained when they are reported fully and also transparently so that readers can assess the strengths and weaknesses of the investigation undertaken. On this pretext, initially QUOROM statement was developed. QUOROM stands for Quality of reporting of Meta-Analysis. It was developed in 1996 and published in 1999 and was conceived as a reporting guide for authors who are reporting a Meta-analysis of randomized trials. Since, there has been a lot of development and expansion in the reporting of systematic reviews but still with all the shortcomings in QUOROM, it was far from ideal and this prompted the need for update. PRISMA came into light with a broader application than the original QUOROM statement and addressed conceptual and methodological issues in greater depth; PRISMA being a development of QUOROM.
Development of PRISMA
The PRISMA statement was developed by a group of 29 review authors, methodologists, clinicians, medical editors and consumers. In the year 2005, over three days long meeting followed by long correspondence meetings a 27 items checklist and a four phase flow chart diagram was developed. All the items found to be necessary in the transparent reporting of systematic review were included in the checklist that was created. The flowchart which was initially proposed for QUOROM was updated, modified to reflect the identified records. Further, after many reviews the flow chart was approved for final inclusion in PRISMA

The 4 stages of a PRISMA flow diagram
The work described in the flow diagram is split into 4 stages:
1.Identifying the articles for review
2.Screening the articles for review
3.Deciding on the studies’ eligibility
4.Finalizing the list of studies to include in the systematic review

1) Identification of the Articles for Review:
In the preliminary stage, you need to take up a search that you have designed through the abstract and citation database that has been selected by you. These could be Scopus, PubMed or any other reliable database. Make a note of the number of records that have been returned by your search. You can also list down the searches you made from different sources such as Google Scholar or even the reference list you can retrieve from other related and relevant articles.
A few important things to take care of at this stage is that one cannot deploy the same search techniques for all databases. Each database has its own unique and specific guidelines that you must adhere to when trying to search relevant articles for review. There are techniques on how to combine keywords or search for keywords of interest that are different for databases. PubMed, for instance, follows a very literal pattern in its search function. If you search the word “medicine” in its titles, you won’t get the list if those titles that include the plural form “Medicines” also. Once you have run searches across all relevant databases you need to combine all shortlisted articles or records under a single citation management program. Google Sheets or Excel can also do a good job of it as conventional tools, but now more sophisticated options are available, such as:
DistillerSR
EndNote
Mendeley
Sciwheel
Despite all care taken, there is a possibility of duplication of records, and you must ensure to remove all duplicate records. Microsoft Excel gives a very handy option in the data tab, which is “Remove Duplicates”. You will just have to specify the column heading as the identified one which you want to select for sorting duplicates.
A very significant suggestion here is to sort the identifiers by DOI. This is because DOI is completely unique in nature. It is a possibility that two articles can have the same titles and in case you delete by sorting on duplication of titles, you may lose an important source for review but by using DOI for sorting this problem can be eliminated. At this stage, you must note that, in the end, how many unique records you are left with.

2) Screening the articles for Review:
At this stage, the researchers go through all the titles and abstracts. By reading each of the articles they can determine whether they contain material which is relevant or helpful to the systematic review. If you decide to exclude articles, you must note down the reason for exclusion and categorize articles based on the reason for which you have decided to not include them in the systematic review. This is a simple “yes/no” choice.
Some of the reasons can be

The article does not have any original data
Absence of control group
The article has no relevance with your research question
There is a mismatch of the population characteristics
 The article is opinionated in nature
Make a note of the number of articles that you excluded and the number of articles under each category of exclusion.
When there is more than one investigator who are working on doing the systematic review, they may decide to not split the articles or divide the workload. If two investigators are there, then both screen every article and abstract, and then they compare their individual decisions. In a situation where there is a difference of opinion about the inclusion or exclusion of a particular article, they both go through the text together and arrive at a mutual decision. In case of confusion, they may ask the principal investigator or project manager o take a call for a specific article.
Do not miss the references of those articles you decide to exclude from your systematic review. They may contain some useful research studies that you can include in your additional records.
3) Deciding on the studies’ eligibility:
Till the second state of screening, the decision about the inclusion or exclusion of an article is taken based on the title and abstract. After having done that, at this stage those articles that get shortlisted are read in full length. The purpose of doing this is to identify whether these articles would help you to answer your research question. In case of two investigators, both perform the full text eligibility screening test and decide to whether to retain or exclude an article. Like the earlier stage, here you must build categories under which you must list down the articles. This clearly specifies the reasons for including or excluding that article after full text analysis. Again, in case of disagreements at this stage, a third person intervention can help in making the right decision about keeping or doing away with a specific article.
4) Finalizing the list of studies to include in the systematic review:
By this stage, you would know clearly about the studies that will be included in your systematic review after eliminating those that are irrelevant to your research question. Make note of this number in your flow diagram. The purpose of this last stage of the diagram is to determine how many of those studies can be included in the quantitative synthesis which in other words is also labelled as meta-analysis. It is possible from all the studies you have shortlisted for your systematic review, not all are eligible for meta-analysis. Meta-analysis is statistical in nature and pools up the data from multiple studies to test the hypotheses. It is quite likely that not all shortlisted studies will have the data that is important for quantitative synthesis. The studies that qualify for meta-analysis must be noted down at the bottom of the flow diagram.
The Assessment of PRISMA
The quality of reporting of the systematic reviews is still not optimal. Survey and analysis has revealed the existence of possible publication bias and its impact on the systematic review. The results are not less than overwhelming. Systematic review does address the issue of publication bias to a large extent but there is no certainty that the investigator or reviewer has done his job of assessment and interpretation fairly. If the researcher brings up an issue of publication bias while performing a systematic review, it is an indication of job done thoroughly. Sometimes investigators show absence in reporting such assessment which does not really mean the absence of it in the process. It can also be attributed to the negligence of the researcher.
Over the years, since the inception of systematic reviews, its application has broadened and it can now be applied to a large array of questions. For instance, now they are conducted to investigate cost-effectiveness, for questions related to diagnostic or prognostics, genetic studies and of course policy making. Prisma covers a general framework of concepts and topics that can be relevant to any systematic review and not just the initial objective of basic healthcare interventions. Still, there is a copy of enhancement and improvement for specific circumstances. The flow diagram would need interventions and adjustments depending on the source of data and the requirement to conduct a Meta-Analysis.
There is also an availability of an explanatory document for increasing the usefulness of PRISMA. For each of the items on the checklist, the supporting document gives an example of good reporting, a rationale that justifies its inclusion, and also the supporting evidence wherever possible. This supporting document can be of great help to those using PRISMA for the first time and also those who are into teaching systematic review methodology to others.
Key drawbacks of PRISMA
When an investigator creates the PRIMA Flowchart manually there are a number of pain points associated with it. Some of the main challenges are:
1) Time Consumption: Preparing a flow diagram for a systematic literature review is a very time-consuming and tedious task. Because of this sometimes it does not do significant value addition to the activity. The time and expertise of these extremely skilled resources had to be targeted toward the actual analysis of data rather than the time that is wasted on the collection and standardization of data. The extraordinary consumption of time in doing this systematic analysis sometimes brings dawn its quality and applicability.
2) Scope of human error: PRISMA is a manual process that makes the flow diagrams inconsistent. Human errors are common and easy to occur this sometimes brings down the quality of the technique
3) Complex Search activity: When doing the manual process, one must search individual databases such as google scholar, Scopus, PubMed etc to locate relevant articles and then export and compile them into one single data set manually. This can be extremely tedious and complex to do and because of this a lot of PhD scholars and clinical practitioners are not able to find the time and effort to take up the activity.
4) Vast Applicability: The application of PRISMA is quite broad though, but still there are many domains of study where its application is still not commonly accepted and used by investigators. Because of this, its scope gets limited in its applicability
5) Can create a difference of opinion in amongst investigators: Many times in the process when it comes to rejection or inclusion of a study, there may be differences of opinion amongst the researchers and that can sometimes sour their professional relations or harbor grudges that can further impact the quality of their subsequent work together.
Conclusion:
PRISMA is a living document with scope for improvement and revisions for better usefulness and application. The. continuous development of the diagram and its checklist will expand its application and usefulness across different research genres.