Most medical experiments are reviewed by groups known as Institutional Review Boards (IRBs); according to every standard account of medical research ethics, an IRB should not approve an experiment unless it has an acceptable combination of risks and benefits. This requirement is often stated in different terms. Some codes say that an experiments benefits to individuals and society must outweigh its risks. Others say that the experiment must have a favorable risk-benefit ratio. The Code of Federal Regulations says that risks must be reasonable in relation to the expected benefits.
However, even though everyone agrees that an experiment must have an acceptable combination of risks and benefits, almost nothing has been said about what it would mean to weigh risks against benefits, compute risk-benefit ratios, or figure out if an experiments risks are reasonable.