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.
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 two references that it thought were the same. The reference on the left has been added to your screening list, while the reference on the right was detected as a duplicate.
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.
Unfortunately, it is not currently possible to manually mark duplicates. In this instance, a good workaround is to create a customized tag which indicates that a reference is a duplicate. You can then vote to exclude it, and use the filter by tag option later on to quickly get a count of how many references were tagged as a duplicate.
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