We recognize that it may be difficult to determine whether two or more closely related protocols should be considered a single study. Generally, if you have research activities that use the same human subjects population, follow the same core research protocol and procedures, and intend to combine the data for analysis in aggregate, this would be considered a single study for the purposes of the PHS Human Subjects and Clinical Trial form.
When in doubt, at the time of application NIH supports grouping studies that use the same research protocol and the same human subjects population into a single study record, to the extent that the information provided is accurate and understandable to NIH staff and reviewers. You are also encouraged to discuss how to group your studies with your NIH Program Officer.
For studies that will need to register and report in ClinicalTrials.gov, keep in mind that each ClinicalTrials.gov record should be a unique study record in the PHS Human Subjects and Clinical Trial form.
Additional FAQs provide handy tips for using the PHS Human Subjects and Clinical Trial Information form.