Which of the following best describes when a protocol may be eligible for expedited review by the IRB?

A protocol is eligible for expedited review by the Institutional Review Board (IRB) primarily when it involves no more than minimal risk to participants and fits within one of the specific categories established for expedited review by federal regulations. This means that the nature of the research poses limited risk to individuals, which allows for a quicker review process rather than a full board meeting.

Funded research or the number of participants, while they may influence the overall nature of a study, do not directly determine eligibility for expedited review. The essence of expedited review is focused primarily on the risk level associated with the research and whether it meets the criteria set forth by federal guidelines, not on funding sources or sample size alone. Additionally, an observational study could still involve minimal risk, but that alone does not qualify it for expedited review if it does not meet the other federal criteria. Hence, the correct choice is notable for encapsulating the core elements that govern the eligibility for expedited review in research protocols.