1: What are duplicate search results?
If search several resources and databases for the same research question, you will definitely have several duplicate search results.
If the bibliographic information of two references or papers or search results is the same, we consider them as duplicate. If you are using bibliographic management programs such as EndNote, you could see such duplicates if you sort the references by title.
*Bibliographic information varies depending on the type of the reference. For a journal paper, the bibliographic information is: Authors’ Names, Title of the Paper, Name of the Journal, Volume and Issue of the Journal and the Pages in which the paper has been published. DOI, PMID, Abstract, etc. might be counted as bibliographic information as well.
2: Why are there duplicates among the search results?
As the amount if academic literature is growing, it is impossible to check every single journal to keep updated. That’s why bibliographic databases such as MEDLINE, EMBASE, CINAHL, and PsycINFO trying to collect the bibliographic information of papers published in each journal to let you search them all in one place within one database – so called ‘indexing’.
To make the papers more and more visible, the journals try to get indexed in as many important databases as they can. It means if you search several medical databases for the same research question, you will find the same paper several times because the journal has been indexed in more than one database.
3: How to find and remove the duplicates?
There are several ways to remove the duplicates.
3.1: Removing the duplicates in databases while searching
If you consider MEDLINE as the core database for your search, you can remove MEDLINE records while searching CINAHL or PubMed also you could delete the results of MEDLINE journals from EMBASE or limit your search to EMBASE when searching EMBASE.
These methods look cool however there is a major problem with all of them that is how do we know that following these methods we are actually deleting the duplicates and these methods are working well? We don’t know really!
3.2: Removing the duplicates using duplicate detection feature in reference management programs
If you are using EndNote or any other reference management program, you could define what a duplicate is and the program could detect and display the duplicates to you so that you could decide and delete the duplicate records.
3.3: Manual Removal of the duplicates in reference management programs
If you sort your references based on the Title within your reference management program and check them, you could detect and delete them manually. If the the search results are a lot, this method will be very time-consuming.