of funds, or because of decisions made by insurance companies. The American Supreme Court approved paying doctors to ration care, saying that there must be "some incentive connecting physician reward with treatment rationing". Shortages of organs for donation forces the rationing of organs for transplant even where funding is available. Credit rationing Credit rationing describes a situation wherein a bank limits the supply of loans, even when it has enough funds to loan, and the provision of loans has not yet equaled the demand of prospective borrowers. Changing the price of the loans (interest rate) does not balance loan demand and supply. Carbon rationing Personal carbon trading refers to proposed emissions trading schemes under which emissions credits are allocated to adult individuals on a (broadly) equal per capita basis, within national carbon budgets. Individuals then surrender these credits when buying fuel or electricity. Individuals wanting or needing to emit at a level above that permitted by their initial allocation would be able to engage in emissions trading and purchase additional credits. Conversely, those individuals who emit at a level below that permitted by their initial allocation have the opportunity to sell their surplus credits. Thus, individual trading under Personal Carbon Trading is similar to the trading of companies under EU ETS. Personal carbon trading is sometimes confused with carbon offsetting due to the similar notion of paying for emissions allowances, but is a quite different concept designed to be mandatory and to guarantee that nations achieve their domestic carbon emissions targets (rather than attempting to do so via international trading or offsetting). Rationing mechanisms The purpose of rationing is to guarantee a minimum of some resource or to impose a maximum limit on its use. (The latter is the case with carbon rationing, where the scarcity is artificial). Usually, the government determines a fair ration, for example, one proportional to the number of family members. If participants possess different rights to a portion (even when they have the same need) and there is not enough for everyone, then one of the many algorithms for solving the bankruptcy problem may apply. At other times, the ration can only be estimated by the beneficiary, such as a factory for which energy is to be rationed. In such cases, a mechanism is needed to discourage misreporting the needs or wants (i.e., to meet strategy-proofness). Suppose every participant reports an ideal ration. For so-called