Systematic Reviews

Role of the librarian in this stage

A librarian can advise you on study selection for your systematic review, including: 

  • How to use Covidence to screen citations and manage the screening process
  • How to apply your review inclusion and exclusion criteria to the screening process

Contact HSL About Your Review

Email us

Ready to start a systematic review? HSL Librarians can help!

Fill out the Systematic Review Request Form and the best-suited librarian will get back to you promptly. Our systematic review service is only available to faculty, staff, students, and others who are affiliated with UNC Chapel Hill.

Screening Results with Covidence

We recommend that systematic review teams use Covidence to screen results. Covidence is provided free from HSL and its partners, and there is no limit to the number of reviews that can be created.

How does screening work in Covidence?

Once you have completed literature searching and compiled all citations, it is time to screen the results. The purpose of screening is to eliminate studies that do not meet your inclusion criteria. Two independent reviewers should screen all studies, starting with a title and abstract screening, followed by a full-text screening. A third reviewer should resolve any conflicts.

During the title/abstract screening, for each reference, each reviewer should read the title and abstract and make a decision:

  • No: This article does not meet inclusion criteria and should not be included in the systematic review.
  • Maybe: There is not enough information in the title/abstract to make a decision (move to full-text screening stage).
  • Yes: This article appears to meet inclusion criteria and should move to the full-text screening stage.

During the full-text screening, for each reference, read the full-text and make a decision:

  • Include: This article meets inclusion criteria and should be included in the systematic review.
  • Exclude: This article does not meet inclusion criteria and should not be included in the systematic review.

Remember, all voting should be blinded, meaning team members should be unable to see how others cast their votes.

PRISMA statement

"PRISMA stands for Preferred Reporting Items for Systematic Reviews and Meta-Analyses. It is an evidence-based minimum set of items for reporting in systematic reviews and meta-analyses. The aim of the PRISMA Statement is to help authors improve the reporting of systematic reviews and meta-analyses. The PRISMA Statement consists of a 27-item checklist and a four-phase flow diagram." (From prisma-statement.org )


PRISMA and Covidence:

Covidence will track numbers of citations screened at each stage and how many are ultimately included in the review. These numbers can be copy and pasted into a PRISMA diagram template. A step-by-step guide on creating a PRISMA diagram is shown below.

Which PRISMA 2020 Flow Diagram should I use?

In PRISMA 2020, there are now expanded options depending on where you search and whether you are updating a review. Version 1 of PRISMA 2020 includes databases and clinical trial or preprint registers.  Version 2 includes additional sections for elaborating on your grey literature search, such as searches on websites or in citation lists.  Both versions are available for new and updated reviews from the Equator Network's PRISMA Flow Diagram page.

Templates for New Reviews

PRISMA 2020 V1 - Databases and Registers PRISMA 2020 V2 - Databases, Registers, and Grey Literature 

The PRISMA diagram for Databases and Registers follows the same format as the previous 2009 PRISMA diagramThe PRISMA diagram for Databases, Registers, and Grey Literature has an additional column on the right side of the diagram for reporting of grey literature searches and results

The PRISMA diagram for Databases
and Registers
follows the same format
as the previous 2009 PRISMA diagram
The PRISMA diagram for Databases, Registers, and Grey Literature
has an additional column on the right side of the diagram for
reporting of grey literature searches and results

Step-by-step: PRISMA 2020 Flow Diagram

Step 1: Preparation To complete the the PRISMA diagram, save a copy of the diagram to use alongside your searches. It can be downloaded from the PRISMA website

Step 2: Doing the Database Search Run the search for each database individually, including ALL your search terms, any MeSH or other subject headings, truncation (like hemipleg*), and/or wildcards (like sul?ur). Apply all your limits (such as years of search, English language only, and so on). Once all search terms have been combined and you have applied all relevant limits, you should have a final number of records or articles for each database. Enter this information in the top left box of the PRISMA flow chart. 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, CENTRAL, ICTRP, or others, you should enter that number after the equal sign in Registers (n=).

NOTE: Some citation managers automatically remove duplicates with each file you import.  Be sure to capture the number of articles from your database searches before any duplicates are removed.

 

Records identified from databases or registers

 

Step 3: Remove All Duplicates To avoid reviewing duplicate articles, you need to remove any articles that appear more than once in your results. You may want to export the entire list of articles from each database to a citation manager such as EndNote, Sciwheel, Zotero, or Mendeley (including both citation and abstract in your file) and remove the duplicates there. If you are using Covidence for your review, you should also add the duplicate articles identified in Covidence to the citation manager number.  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.

Records removed before screening: duplicates, automation tool exclusions, or other reasons

NOTE: If you are using Covidence to screen your articles, you can copy the numbers from the PRISMA diagram in your Covidence review into the boxes mentioned below.  Covidence does not include the number of results from each database, so you will need to keep track of that  number yourself.

Step 4: Records Screened- Title/Abstract Screening The next step is to add the number of articles that you will screen. This should be the number of records identified minus the number from the duplicates removed box.

Number of records screened in Title/Abstract level

 

Step 5: Records Excluded- Title/Abstract Screening You will need to screen the titles and abstracts for articles which are relevant to your research question. 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 in the box to the right titled "Records excluded."  You can optionally add exclusion reasons at this level, but they are not required until full text screening.

Records excluded after title & abstract screening

 

Step 6: Reports Sought for Retrieval This is the number of articles you obtain in preparation for full text screening.  Subtract the number of excluded records (Step 5) from the total number screened (Step 4) and this will be your number sought for retrieval.

Reports sought for retrieval

Step 7: Reports Not Retrieved List the number of articles for which you are unable to find the full text.  Remember to use Find@UNC and Interlibrary Loan to request articles to see if we can order them from other libraries before automatically excluding them.

Reports not retrived

Step 8: Reports Assessed for Eligibility- Full Text Screening  This should be the number of reports sought for retrieval (Step 6) minus the number of reports not retrieved (Step 7). Review the full text for these articles to assess their eligibility for inclusion in your systematic review. 

Reports assessed for eligibility

 

Step 9: Reports Excluded 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.  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 if meets multiple exclusion criteria.

Reports excluded, including reason for exclusion and number

 

Step 10: Included Studies The final step is to subtract the number of records excluded during the eligibility review of full-texts (Step 9) from the total number of articles reviewed for eligibility (Step 8). Enter this number in the box labeled "Studies included in review," combining numbers with your grey literature search results in this box if needed.  You have now completed your PRISMA flow diagram, unless you have also performed searches in non-database sources.

Studies included in review
 
If you have also searched additional sources, such as professional organization websites, cited or citing references, etc., complete the additional steps listed in the following box Documenting Your Grey Literature Search.

Updating a systematic review with PRISMA 2020

PRISMA 2020 templates for updated reviews include a box for the number of studies and reports included in the previous version of the review.


If you are updating an existing review, use one of these PRISMA 2020 Updated Review templates, which feature an additional box for the number of studies and reports of studies included in the previous search iterations.

Documenting Your Grey Literature Search

To document your grey literature search, download the flow diagram template version 1 PRISMA 2020 flow diagram for new systematic reviews which included searches of databases, registers and other sources or the version 2 PRISMA 2020 flow diagram for updated systematic reviews which included searches of databases, registers and other sources.  Complete the boxes documenting your database searches on the left side of the template as outlined in the previous box Step-by-step: PRISMA 2020 Flow Diagram.  Complete the right side of the template, Identification of studies via other methods, using the steps below.
 
Step 1: Records Identified If you have identified articles through other sources than databases (such as manual searches through reference lists of articles you have found or search engines like Google Scholar), enter the total number of records from each source type in the box on the top right of the flow diagram.
Records identified from websites, organizations, citation searching, or other methods
 
Step 2: Reports Sought for Retrieval This should be the total number of reports you obtain from each grey literature source. 
Reports sought for retrieval
 
Step 3: Reports Not Retrieved List the number of documents for which you are unable to find the full text.  Remember to use Find@UNC and Interlibrary Loan to request items to see if we can order them from other libraries before automatically excluding them.
Reports not retrieved
 
Step 4: Reports Assessed for Eligibility This should be the number of grey literature reports sought for retrieval (Step 2) minus the number of reports not retrieved (Step 3). Review the full text for these items to assess their eligibility for inclusion in your systematic review. 
Reports assessed for eligibility (full text)
 
Step 5: Reports excluded After reviewing all items 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 item as well as the number of items excluded for each reason.  Examples include wrong setting, wrong patient population, wrong intervention, wrong dosage, etc.  You should only count an excluded item once in your list even if if meets multiple exclusion criteria.
Reports excluded, with reasons for exclusion and number

 

Step 6: Included Studies The final step is to subtract the number of excluded articles or records during the eligibility review of full-texts from the total number of articles reviewed for eligibility. Enter this number in the box labeled "Studies included in review," combining numbers with your database search results in this box if needed.  You have now completed your PRISMA flow diagram, which you can now include in the results section of your article or assignment.

Studies included in review