For en mer omfattende diskusjon, se Joint Committee on Taxation, Current Law and Background on Federal Tax Provisions Relating to Retirement Savings Incentives, Health and Long-Term Care, and Estate and Gift Taxes (JCX-29-99), 15. juni 1999.
Boken "Joint Committee on Taxation, Present Law and Background on Federal Tax Provisions Relating to Retirement Savings Incentives, Health and Long-Term Care, and Estate and Gift Taxes" har mer informasjon om dette.