The UC San Diego IRB/HRPP defines enrolled as an eligible, appropriately informed individual agreeing to participate in a study. For instance, when an individual signs an informed consent document, that individual is considered enrolled in the study. It is this definition of enrolled that should be used to determine the number of participants to be enrolled as indicated on all study documents including the Application Facesheets, the Research Plan, consent/permission/assent documents, Continuing Review Facepages, etc.
Further, this definition allows for consistency of enrollment review across all projects and ensures that for studies that may include "screening procedures," the individual is "enrolled" in the study to allow these study procedures to be done.
Why define "enrolled" this way? Current federal guidelines include that at the time of continuing review, "the IRB's responsibility to protect human subjects should include the IRB's review of trial progress. For example, expected rates of enrollment and dropout are generally identified for most studies. A marked difference between the actual and expected rates of enrollment or dropout, either at an individual site or in the study as a whole, may indicate a problem requiring further investigation."
The guidelines also include, "As part of its initial review, the IRB will have approved the protocol, which typically includes the number of subjects expected to be enrolled at a particular site. An investigator who enrolls more subjects than the number allowed at that site may have violated the study protocol or conditions set by the IRB or FDA…. Information about the number of subjects enrolled in the overall study may allow the IRB to ascertain whether enrollment is consistent with the planned number of subjects described in the approved protocol. If enrollment in the study as a whole is too low (either because subject enrollment is too low or subject withdrawal is too high), there may not be justification to continue exposing subjects to the risks of the test article because the study itself may no longer be expected to provide sufficient data to answer the scientific question at hand."
The IRB/HRPP recognizes that commercial sponsors, and others, may have a different definition, such as considering an individual "enrolled" in a study when the participant has been assigned to a study arm or has taken their first dose of the study drug. If the sponsor provides such definition, the PI may include that description and expected number under that definition in the Research Plan. For instance, the Research Plan may include, "The study sponsor considers enrollment in the study to be when the participant has received their assignment to a study arm, which occurs at study visit 2."
However, as noted above, the study documents including Application Facesheets, Research Plan, and consent/permission/adolescent assent documents, Continuing Review Facepages, etc, must reflect the enrollment number of those individuals who are eligible, appropriately informed and agree to participate in a study.