Deduplication of database exports 9medline, psycinfo, web of science etc) for systematic reviews and meta analyses

1. zoteroBefore you start;
• Prepare the files for importing into Zotero
• When exporting from databases, look for the RIS files option, or the
‘other reference software’ option
• Name your files with database info and number of results. This will
come in handy later. Especially for databases that do not allow more
than 500 results per export because you’ll need to do multiple
exports (e.g. PsycINFO1_500, PsycINFO501_1000 etc.)

2. Import your files into Zotero
NB. Zotero will create a separate folder per import

3. When you’re finished, create a new folder for all files

4. Copy the results from every database folder
into the ‘all files’ folder
1. To select all, click on a record, and press Ctrl + a
2. Drop and drag the selected files into the ‘all
files’ folder

5. 843 results
+
The sum of the separate folders should match the ‘all files’ folder
(To select all, click on a record, and press Ctrl + a)

6. From the ‘all files’ folder, click on ‘Duplicate Items’
1
2

7. In order to make deduplication easier,
select year, issue, pages and volume

8. First, merge all the items that are obvious duplicates (e.g. page
numbers). Then spend more time on the difficult ones (next slide)

9. Compare references
• Click on the different versions in order to
compare
• Doi’s
• Abstracts (click on the abstract to view short or long version)
• Are the titles equally long?
• drag the bar at the top
• Different item types, but same reference?
• Change the reference type of one of the items, then merge
• Add other fields like Publication (journal name)

10. Nice to know
• Zotero currently uses the the title, DOI, and ISBN fields
to determine duplicates. If these fields match (or are
absent), Zotero also compares the years of publication
(if they are within a year of each other) and
author/creator lists (if at least one author last name
plus first initial matches) to determine duplicates. The
algorithm will be improved in the future to incorporate
other fields.
• You should always resolve duplicate items by merging
them, rather than deleting one of the duplicates.
Merges will retain all of the collections and tags of the
merged items; deleting one item will lose these data.
• Zotero help: https://www.zotero.org/support/start
or email j.p.c.staaks@uva.nl