The principle of clinical equipoise aims to ensure that research subjects are not exposed to risks without the possibility of benefit. It requires that there be genuine uncertainty in the expert medical community about the comparative therapeutic merits of each arm of the trial. Miller and Brody criticize clinical equipoise as too vague and difficult to apply consistently. Warren's view that personhood occurs later than birth could imply that abortion and infanticide may be morally permissible in some cases. However, allowing abortion and infanticide raises ethical concerns about protecting the lives and rights of vulnerable human beings.