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Gerstein Science Information Centre

Searching the Literature: A Guide to Comprehensive Searching in the Health Sciences

Students and researchers in the health sciences are often required to conduct comprehensive searches of the literature. Follow the steps in this guide to learn how this process works.

Updating Your Search

According to the Cochrane Handbook, searches must be rerun close to publication, if the initial search date is more than 12 months (preferably six months) from the intended publication date, and the results screened for potentially eligible studies - 4.4.10 Timing of searches. 

 

To update your search, we recommend:

  • rerunning your saved database search strategies to find any records that have been newly added to the databases
    • this may include both newly published records as well as older records that have only recently been added to a database
  • check for changes to any database-specific subject headings. For instance, MeSH terms are updated annually. 

This page outlines two main strategies that you can use to update a search:

  1. The first involves deduplicating new result sets in Covidence.
  2. The second involves limiting the indexing dates in specific databases. The aim of both methods is to retrieve newly available records without needing to screen all search result records again. 

Updating Your Search Using Covidence

BEFORE you update your results in Covidence, make sure you download your original PRISMA flowchart so that you have a record of the original numbers:

  1. click the PRISMA box in the top right corner of the "Review Summary" page
  2. click "Download DOCX" in the top right corner of the following page

How to Update your Results Using Covidence:

  1. rerun all your saved search strategies in each database as you did in your original search
  2. export all records from each database as an .RIS file (you may need to batch export depending on how many total results are retrieved by the search)
  3. next, import the new RIS files from the rerun searches into "Title and abstract screening."

The records will be automatically deduplicated against the original import, and any new records will appear in the "Title and abstract screening" stage. 

Visit the How to update a review with new studies page from Covidence for more detailed instructions or watch the video tutorial below. 

Updating Your Search Using Database Indexing Dates

Another method is to limit the indexing dates in each specific database when you rerun your saved search strategies.

Note that the indexing date is the date the record was added to the database not the publication date. Remember that you are looking for any records that have been added to the database after your initial search, regardless of their publication date. 

 

The indexing date field differs between databases and is unfortunately not available in all databases. The table below provides search strings or filters to combine with your saved search strategies in Cochrane CENTRAL, PubMed, Ovid MEDLINE, Ovid Embase, Ovid PsycInfo, Ebsco CINAHL, Scopus, Web of Science Core Collection, and ClinicalTrials.gov. 

We recommend double checking the field code information from each database as they are subject to change. 

Note: in the table below, x refers to the final row of your search.

Database

Search Fields and Example of a search last run on July 9, 2023 and updated March 19, 2025

Cochrane CENTRAL (Trials)

Use "Date" filter

"Date added to CENTRAL trials database" NOT "Year first published" 

Example:

  • View search results 
  • Select "Trials" tab 
  • On the "Filter your results" menu (left-hand side), navigate down to "Date" (NOT "Year")
  • Enter custom date range: 09/07/2023 to 19/03/2025
PubMed

CRDT or EDAT or MHDA

CRDT refers to Create Date, EDAT refers to Entry Date, and MHDA refers to the date that MeSH are added (MHDA may increase duplicates but can identify indexed records previously missed by textword searching). 

Example: 

#x AND ("2023/07/09"[CRDT] : "3000"[CRDT] OR "2023/07/09"[EDAT] : "3000"[EDAT] OR "2023/07/09"[MHDA] : "3000"[MHDA])
Ovid MEDLINE

.dt,ez,da.

dt refers to Create Date, ez refers to Entrez Date, and da refers to MeSH date (da may increase duplicates but can identify indexed records previously missed by textword searching). 

Example: 

x AND (202307* OR 202308* OR 202309* OR 20231* OR 2024* OR 2025*).dt,ez,da. 
Ovid Embase

limit x to dc=YYYYMMDD-YYYYMMDD

dc refers to Date Created. 

Example: 

limit x to dc=20230709-20250319
Ovid PsycInfo

limit x to up=YYYYMMDD-YYYYMMDD

up refers to Update Code (the date the record was released into the database). 

Example:

limit x to up=20230709-20250319
Ebsco CINAHL

EM YYYYMMDD- OR (ZD "in process" AND RD YYYYMMDD-)

EM refers to Entry Date and is followed by the original search date and a hyphen to retrieve records entered on or after that date. ZD "in process" refers to records that are in the process of being indexed. RD refers to Release Date.

Example:

Sx AND (EM 20230709- OR (ZD "in process" AND RD 20230709-))
Scopus

ORIG-LOAD-DATE AFT yyyymmdd

Fill in date as one day BEFORE the date of your original search.

Example:

AND ORIG-LOAD-DATE AFT 20230708

Limits search results to records added AFTER July 8, 2023.
Web of Science Core Collection

Method 1: Enter Index Date in YYYY-MM-DD format via "Advanced Search" > "Add date range" > "Index Date" > "Custom"

Method 2: Use LD=(YYYY-MM-DD/YYYY-MM-DD) in the Query Preview box via "Advanced Search" > "Query Builder" > "Query Preview"

Example: 

Method 1:

  • Select "Add date range" from underneath the Query Preview box 
  • From the dropdown menu, navigate to "Index Date" and select "Custom"
  • Enter custom date range: 2023-07-09 to 2025-03-19

Method 2:

Type directly into the Query Preview box at the end of your search string: AND LD=(2023-07-09/2025-03-19)
ClinicalTrials.gov

Use the "First posted" date field

Example: 

  • Select "More Filters"
  • Navigate down to "Date Range"
  • Under "First posted" enter custom date range: 09/07/2023 to 19/03/2025

Adapted from: https://libraryguides.mcgill.ca/knowledge-syntheses/updating

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