====== Trial Registries for Systematic Reviews ======

=== What Are Trial Registries? ===
Trial registries are publicly accessible databases that list clinical trials, including ongoing, completed, and unpublished studies. Searching them helps minimize **publication bias** and identify **grey literature**.

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=== Major Trial Registries to Search ===

  * **ClinicalTrials.gov**  
    https://clinicaltrials.gov  
    Largest global registry maintained by the U.S. National Library of Medicine. Covers trials worldwide.

  * **WHO International Clinical Trials Registry Platform (ICTRP)**  
    https://trialsearch.who.int  
    Aggregates multiple national and regional registries into a single search portal.

  * **European Union Clinical Trials Register (EUCTR)**  
    https://www.clinicaltrialsregister.eu  
    Contains interventional clinical trials conducted in the European Union and European Economic Area.

  * **ISRCTN Registry**  
    https://www.isrctn.com  
    A primary clinical trial registry recognized by WHO and ICMJE.

  * **Chinese Clinical Trial Registry (ChiCTR)**  
    http://www.chictr.org.cn  
    Primary registry for trials conducted in China.

  * **Clinical Research Information Service (CRiS)**  
    https://cris.nih.go.kr  
    South Korean clinical trials registry.

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=== How to Search Trial Registries ===

  * Use broad keywords and synonyms related to your PICO question.
  * Filter by study status (e.g., recruiting, completed).
  * Export results where possible for screening.
  * Document search date, strategy, and results as part of your review.

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=== Why Search Trial Registries? ===

  * Identify unpublished or ongoing trials to reduce **publication bias**.
  * Access detailed protocols, sample sizes, and outcomes.
  * Check for **discrepancies** between registered protocols and published reports.