Covidence automatically de-duplicates upon import. The de-duplication mechanism checks both within the file being uploaded as well as against all previous imports.

To identify duplicate references, Covidence checks on title, year, and volume, all of which must match exactly, and the authors must be similar.


Reviewing duplicates

You can view the duplicates from the Imports >> Import History page. Click "Check duplicates" under the import listed to see the references that were taken out.

Covidence will show you references that it thought were the same.  The primary reference on the left has been added to your screening list, while the references on the right have been detected as duplicates.


If any were removed by mistake you can click "not a duplicate" and they will be restored to your reference list.


What if there are still duplicates in my screening list?

Because Covidence uses a very strict de-duplication method, it has the benefit of rarely, if ever, taking out duplicates mistakenly, but can have the side effect of missing some that a reference manager program may have been able to detect.

In the Title and Abstract or Full text stage, you have the option to mark a reference as a duplicate. This will automatically: 

  • Remove it from the screening list
  • Report it as a duplicate in the PRISMA diagram
  • Excluded it from the inter-rater reliability report if a vote has already been cast on the reference and;
  • Show who marked the reference as a duplicate

If you make a mistake, then you can quickly undo or manage this later on the manually marked duplicates page.



Sometimes the data belonging to a particular reference is corrupt and Covidence is unable to import the reference.  You can view the errors for a particular import from the Import >> Import History page.

Common causes for issues with importing references are as follows:

  • Invalid issue
  • Invalid volume
  • Invalid page numbers
  • An extended Journal name
  • Journal name with additional information
  • Missing typical fields
  • Incompatible formatting