PRISMA-S (PRISMA Search Reporting Extension) is a 16-item checklist that provides detailed guidance for reporting literature search strategies in systematic reviews and related evidence synthesis methods. Published in 2021 by Rethlefsen and colleagues, PRISMA-S extends the standard PRISMA 2020 guidelines by addressing the search component in much greater depth than the 2 search-related items in the main PRISMA checklist. A reproducible, comprehensive search strategy is the methodological foundation of every systematic review, and without it, the entire evidence synthesis is compromised.
PRISMA-S recognizes that search strategies are among the most underreported and poorly documented aspects of systematic reviews. Studies consistently find that published reviews lack sufficient detail for readers to evaluate or replicate the search, which undermines the core principle of systematic review transparency.
Why Search Reporting Matters
The search strategy determines which studies are found, which are missed, and ultimately which evidence informs the review's conclusions. Poor search reporting creates several problems:
- Irreproducibility: Other researchers cannot verify that the search was comprehensive
- Hidden bias: Incomplete reporting may mask a narrow or biased search approach
- Quality assessment failure: Peer reviewers and methodologists cannot evaluate search quality
- Wasted resources: Teams attempting to update the review cannot replicate the original search
The complete PRISMA 2020 reporting checklist addresses search reporting in Items 6 (search strategy) and 7 (information sources), but these items provide general guidance. PRISMA-S expands this into 16 specific items covering every aspect of search documentation.
The 16 PRISMA-S Checklist Items
Database Name (Item 1)
Name each database, platform, or information source searched. Use the official name and specify the platform (e.g., "MEDLINE via PubMed" or "MEDLINE via Ovid," as these are different interfaces with different search functionalities).
Multi-Database Searching (Item 2)
If searching multiple databases simultaneously through a single platform (e.g., EBSCOhost), name each database searched and clarify that they were searched simultaneously.
Study Registries (Item 3)
List any study registries searched (e.g., ClinicalTrials.gov, WHO ICTRP, ISRCTN). Describe the search approach used for each registry.
Online Resources and Browsing (Item 4)
Describe any websites, online collections, or web pages browsed or searched. Include the URL, search method, and date accessed.
Citation Searching (Item 5)
Describe any citation searching performed, whether forward (who cited these studies?) or backward (reference list checking). Specify which studies' reference lists were checked and what tools were used for forward citation searching.
Contacts (Item 6)
Describe any contacts with authors, experts, organizations, or manufacturers to identify unpublished or additional studies.
Other Methods (Item 7)
Describe any other methods used to identify studies, such as handsearching journals, searching conference proceedings, or using social media.
Full Search Strategies (Item 8)
Include the complete search strategy for EVERY database and source searched, not just one. Each strategy should include all search terms, subject headings, Boolean operators, field tags, and limits. Present strategies in an appendix if space is limited.
Limits and Restrictions (Item 9)
Describe all limits applied to searches: date ranges, language restrictions, publication type filters, geographic restrictions. Justify each restriction.
Search Filters (Item 10)
If validated search filters were used (e.g., a randomized controlled trial filter, a diagnostic accuracy filter), name the filter, cite its source, and note any modifications.
Prior Work (Item 11)
Indicate whether the search strategy was derived from or informed by prior reviews, published search strategies, or database-specific search guides.
Updates (Item 12)
Describe the date of the most recent search or search update for each database. If the review was conducted over an extended period, describe when searches were updated and how new results were integrated.
Dates of Searches (Item 13)
Provide the exact date each search was executed. This is critical because database indexing changes over time, meaning the same search may produce different results on different dates.
Peer Review (Item 14)
Describe whether the search strategy was peer reviewed, by whom, and using what method. The PRESS (Peer Review of Electronic Search Strategies) checklist is the recommended tool.
Total Records (Item 15)
Report the total number of records identified from each database or source before deduplication. This information is also captured in your PRISMA flow diagram. Create yours using our PRISMA 2020 diagram maker.
Deduplication (Item 16)
Describe the process used to manage and remove duplicate records. Specify the software or method used and the number of duplicates removed.
Implementing PRISMA-S in Practice
Step 1: Plan Search Documentation from the Start
Do not wait until manuscript writing to document your search. Record every detail as you develop and execute your search strategy. Maintain a search log with dates, databases, strategies, and results for each search session.
Step 2: Work with an Information Specialist
PRISMA-S explicitly recommends involving a librarian or information specialist in search design and execution. Their expertise ensures comprehensive, well-structured strategies and proper documentation. Many institutions provide librarian support for systematic reviews.
Step 3: Use the PRESS Checklist for Peer Review
Before finalizing your search, have it peer reviewed using the PRESS (Peer Review of Electronic Search Strategies) checklist. PRESS evaluates translation of the research question into search concepts, Boolean logic, subject headings, text word terms, spelling and syntax, and search limits.
Step 4: Document Database-Specific Strategies
Each database uses different controlled vocabularies, field tags, and syntax. A PubMed search cannot simply be copied into Embase; it must be translated. Document the translated strategy for every database, not just the primary one.
Step 5: Record All Dates and Numbers
For each database search, record the exact date executed and the number of records retrieved. This enables reproducibility and informs the database-specific counts in your PRISMA flow diagram.
Common Search Reporting Errors
Error 1: Reporting Strategy for Only One Database
PRISMA-S Item 8 requires complete strategies for all databases. Reporting only the PubMed strategy when you also searched Embase, CINAHL, and PsycINFO leaves most of your search undocumented.
Error 2: Missing Platform Information
"MEDLINE" is not sufficient; you must specify "MEDLINE via Ovid" or "MEDLINE via PubMed." Different platforms have different search capabilities and syntax, and the same query may yield different results.
Error 3: No Search Dates
Without exact dates, the search cannot be reproduced or updated. Database content changes daily as new records are indexed.
Error 4: Undocumented Filters and Limits
If you applied a study design filter, language restriction, or date limit, each must be documented and justified. Undocumented limits may appear as hidden bias.
Error 5: No Deduplication Reporting
Simply stating "duplicates were removed" is insufficient. Specify the method (e.g., "automated deduplication using Covidence, followed by manual review") and the number removed.
PRISMA-S and the PRISMA Flow Diagram
PRISMA-S complements the PRISMA 2020 flow diagram by providing the detailed search documentation that the diagram summarizes. The flow diagram shows the total records from each source and duplicates removed. PRISMA-S provides the underlying documentation for how those numbers were generated.
When completing your PRISMA flow diagram, the database-specific counts (Item 15) and deduplication numbers (Item 16) from PRISMA-S directly populate the identification section. For guidance on documenting your protocol, including the search strategy section, see our article on writing a systematic review protocol with PRISMA-P.
Search Strategy Example
Here is a simplified example of a documented search for a systematic review on mindfulness-based interventions for anxiety disorders:
Database: MEDLINE via PubMed Date searched: January 15, 2026 Records retrieved: 1,847
("mindfulness"[MeSH Terms] OR "mindfulness-based"[tiab] OR
"MBSR"[tiab] OR "MBCT"[tiab] OR "mindfulness meditation"[tiab])
AND
("anxiety disorders"[MeSH Terms] OR "anxiety"[tiab] OR
"generalized anxiety"[tiab] OR "social anxiety"[tiab] OR
"panic disorder"[tiab])
AND
("randomized controlled trial"[pt] OR "controlled clinical trial"[pt]
OR "randomized"[tiab] OR "randomly"[tiab] OR "trial"[tiab])
Limits: English language, published 2010-2025, humans Filter: Cochrane Highly Sensitive Search Strategy for RCTs (adapted for PubMed)
This strategy would need to be translated and documented separately for each additional database searched.
Frequently Asked Questions
Is PRISMA-S mandatory for systematic reviews?
PRISMA-S is a recommended reporting extension, not a mandatory requirement. However, journals increasingly expect detailed search documentation, and PRISMA-S provides the standard framework. Following PRISMA-S significantly improves the reproducibility and credibility of your review.
Do I need to include full strategies for every database?
Yes. PRISMA-S Item 8 recommends including the full search strategy for every database searched. Use a supplementary appendix if the manuscript word count is limited, as most journals accept this approach.
What is the PRESS checklist?
PRESS (Peer Review of Electronic Search Strategies) is a standardized tool for peer reviewing search strategies in systematic reviews. It evaluates whether the search adequately translates the research question into search terms, uses appropriate Boolean logic, includes relevant subject headings, and avoids errors. Having your search PRESS-reviewed before execution improves quality.
How do I handle searches that cannot be fully documented?
Some sources (e.g., browsing organizational websites, contacting experts) cannot be documented as reproducible search strategies. For these, describe the process as precisely as possible: which websites were browsed, when, what search terms were used, and what was found. This aligns with the full systematic review methodology approach.
Should grey literature searches follow PRISMA-S?
Yes. Grey literature searches (conference proceedings, thesis databases, organizational websites, trial registries) should be documented following the relevant PRISMA-S items. Even though these searches may not follow formal database syntax, they should be described with enough detail for another researcher to approximate the approach.