CEDAR (CEPI Evidence Discovery And Retrieval)

CEDAR is a standards-based service that supports search, access, and use of patient-centered outcomes research (PCOR) and other research findings across multiple repositories and programs within AHRQ’s Center for Evidence and Practice Improvement (CEPI).

Health IT developers can use CEDAR to integrate AHRQ CEPI research findings directly into their existing systems, where the findings can then be accessed and used by researchers, clinicians, policymakers, patients, and others. CEDAR optimizes the use of PCOR findings and other research data by following standard guidelines for improving the findability, accessibility, interoperability, and reusability (the FAIR principles) of digital assets, providing fast and efficient access to information.

Note: development of CEDAR has paused as of Sept 30, 2023 and the CEDAR API service will be offline while CEDAR is on hiatus. The source code will continue to be available.

The diagram below illustrates the CEDAR components, their users, and external dependencies.

CEDAR Concept of Operations


Client applications can use the CEDAR application programming interface (API) to find and retrieve information about the evidence that CEDAR indexes. An API is a set of rules that describes how two systems communicate with each other. The CEDAR API allows developers to expand existing systems or to create new ones that interact with CEDAR and with resources indexed by CEDAR.

The Clinical Evidence Repositories represent research evidence maintained from various AHRQ programs and encompasses the Systematic Review Data Repository, the Effective Health Care (EHC) Program, CDS Connect, and the U.S. Preventive Services Task Force (USPSTF).

CEDAR was developed as an API rather than as a website to support a wider variety of use cases and to allow CEDAR to be more easily integrated with other systems. The CEDAR API is built using the Fast Healthcare Interoperability Resources (FHIR) standard and utilizes the FHIR Citation resource to represent and share information about indexed artifacts. The CEDAR API works by accepting requests that specify search criteria and responding with all matching resources, termed "artifacts," as FHIR Citations.

The API supports several types of interaction:

  • Searching by Artifact text in the title or body of the artifact; CEDAR automatically includes synonyms when conducting searches by text
  • Searching by Artifact keyword as specified by the source repository
  • Searching by Concept; CEDAR maps Artifact keywords to health Concepts in vocabularies like SNOMED-CT external link icon or MeSH external link icon using the UMLS Metathesaurus
  • Searching by last updated or publication date; CEDAR allows Artifacts to be filtered by the date that CEDAR detects they have been modified or publication date
  • Searching by Artifact status; each Artifact in CEDAR can have a status of draft, active, unknown, archived, or retracted
  • Searching by Artifact publisher; searches can be scoped by the Artifact source repository
  • Retrieving the full list of repositories indexed by CEDAR
  • Navigating through the MeSH Concept hierarchy tree to find relevant Concepts for searching

The CEDAR Demonstration User Interface

A CEDAR Demonstration User Interface was developed to demonstrate CEDAR capabilities, to help guide future development of client applications, and to support pilot testing. A screenshot of the web browser-based user interface is shown below.

CEDAR Demonstration User Interface

CEDAR Source Code

CEDAR was developed as an open-source project. The code is publicly available in the following repositories:

Additional Information

The CEDAR Project Page contains additional information and links to CEDAR project publications.

Contact ClinicalDecisionSupport@ahrq.hhs.gov to learn more about CEDAR.