Clinical trials

Status: Published
Version: 1.0
License: this recommendation document is licensed under CC BY-ND 2.0 UK


JATS4R subgroup. Members (in alphabetical order):
Laura Fullford, PrePress Projects; Melissa Harrison, eLife; Kirsty Meddings, Crossref; Rhiannon Miller, PrePress Projects; Lucie Senn, Frontiers (Chair); Daniel Shanahan, Cochrane



@content-type, @source-type, @source-id, @source-id-type, @document-id, @document-id-type


This document contains best-practice recommendations for capturing clinical trial information in JATS XML. Note that this recommendation applies only to clinical trials on which the article is reporting. Any other clinical trial references that are present should remain as URL links in the text and should not be converted to references/citations or to a <related-object>.

For the purpose of registration, a clinical trial is any research study that prospectively assigns human participants or groups of humans to one or more health-related interventions to evaluate the effects on health outcomes. Interventions include, but are not restricted to, drugs, cells, and other biological products, surgical procedures, radiological procedures, devices, behavioural treatments, process-of-care change, and preventive care. (

Clinical trials are identified by a clinical trial number, which is unique within any given registry but not necessarily unique across registries. Thus, both the registry and the clinical trial number must be provided to accurately identify the clinical trial.

Although editorial decision-making is normally outside JATS4R’s purview, it is recommended that all clinical trials should:

  1. be registered in WHO-approved databases,
  2. be listed on the WHO International Clinical Trials Registry Platform (ICTRP), and
  3. associate a Crossref DOI in the metadata. Crossref provides an API that contains both pieces of information (DOI and Name) and the JATS4R Validator tool will use this to provide warning messages if registries other than the ones listed by Crossref are used.

Note: The International Committee of Medical Journal Editors (ICMJE) has indicated that clinical trials should be listed at the end of the abstract, a recommendation which was based on requirements of visual appearance, rather than on those of machine-readability or XML. Additionally, the ICMJE’s recommendation was made at an earlier time, before there was a need to include so many pieces of additional metadata important to an article. Thus, the ICMJE’s recommendation has not been included as part of this recommendation.

Additional reading


  1. <related-object>. Contain each clinical trial within a separate <related-object> element (i.e. one per clinical trial). The <related-object> element(s) may be contained within any of the following locations
    (1) within the abstract in a separate <sec> or <p>
    (2) directly in <article-meta>
    (3) within the narrative flow

    The information and structure thereof within <related-object> elements is at the content provider’s discretion, as the value of this element is not prescribed here.

    [[Validator tool result: if more than one of each of the attributes and related values, or more than one xref link ERROR]]
  2. @content-type. Use the content-type attribute optionally to indicate which stage of the trial the publication is reporting on. Since this information is intended for content providers submitting linked clinical trial information to Crossref, if @content-type is used, its value must be “pre-results”, “results”, or “post-results”, as defined in the crossref schema. 

    [[Validator tool result: If @content-type present and values not equal “pre-results”, “results” or “post-results” ERROR]]
  3. @source-id. The source-id attribute must be used to identify the clinical trial registry. Crossref curates a list of WHO-approved registries and assigns them a DOI. Content providers are encouraged to select an appropriate registry from this list and supply the registry DOI or the WHO registry name as the source-id value.
  4. @source-id-type. The source-id-type attribute must be used to identify the type of ID provided in @source-id. The value of @source-id-type should be “crossref-doi” or “registry-name”, as appropriate (see point 3 above).

    [[Validator tool result: if the value is “crossref-doi” and @source-id does not contain a Crossref DOI as provided via the Crossref API ERROR]]

    [[Validator tool result: if the value is “registry-name” and @source-id does not contain a registry name from the WHO-defined list WARNING]]

    [[Validator tool result: if @source-id value is not one of the WHO-approved registry dois or names ERROR]]
  5. @source-type. The @source-type should be used to indicate the <related-object> is referring to a clinical trial and the value of “clinical-trial-registry” should be used.

    [[Validator tool result: if no @source-type=”clinical-trials-registry”, and @source-id-type= “crossref-doi” or “registry-name”, and/or @source-id = WHO-approved registry doi or name WARNING]]
  6. @document-id. The document-id attribute is required and must hold the clinical trial number as provided in the clinical trial registry.

    [[Validator tool result: if @document-id is missing ERROR]]

    [[Validator tool result: if @document-id-type=”doi” and @document-id value is not a doi ERROR]]
  7. @document-id-type. The document-id-type attribute is required and must identify the kind of @document-id. The value must be either “clinical-trial-number” or “doi”.

    [[Validator tool result: if @document-id-type is missing, or if the value of this attribute is not “clinical-trial-number” or “doi” ERROR]]


Example 1: Clinical trial at the end of the abstract in a separate section (Crossref DOI)

<sec id="abs3-9">
  <title>Clinical trial registration</title>
 <related-object content-type="pre-results" source-type="clinical-trials-registry" source-id="10.18810/clinical-trials-gov" source-id-type="crossref-doi" document-id="NCT02968459" document-id-type="clinical-trial-number" xlink:href="">
     This study is registered with as NCT02968459.

Example 2: Clinical trial in main article (Crossref DOI)

 <related-object content-type="pre-results" source-type="clinical-trials-registry" source-id="10.18810/isrctn" source-id-type="crossref-doi" document-id="10.1186/ISRCTN98371961" document-id-type="doi" xlink:href="">
     Clinical Trial Registration: This study is registered with ISRCTN as ISRCTN98371961.

Example 3: Clinical trial at the end of the abstract in a separate section (listed registry name) and @id added for those who use the PMC style checker.

<sec id="abs3-9">
  <title>Clinical trial registration</title>
 <related-object id="RO1" source-type="clinical-trials-registry" source-id="" source-id-type="registry-name" document-id="NCT02968459" document-id-type="clinical-trial-number" xlink:href="">
     This study is registered with as NCT02968459.


Working: November 14, 2017 – February 6, 2018

Public review: February 9, 2018 – March 9, 2018

Committee review: March 9, 2018 – May 24, 2018

Published: June 5, 2018

Updated on October 18, 2023

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