The ones that do pay interest resemble ordinary fixed-rate bonds.

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Messrs Feldstein and Samwick also assume that retired folk will convert their personal retirement accounts into a variable-rate annuity, based on a combination of stocks and bonds, rather than a fixed-rate annuity.

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Underlying the rate worries, bonds -- whose fixed return makes them linked to interest rate and inflation expectations - also weakened.

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Things like that could be something as simple as non-traded real estate investment trusts, or secured floating-rate income, as opposed to fixed income or bonds.

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Series I bonds consist of two components: a fixed interest rate return and an adjustable inflation-linked return, making them somewhat similar to TIPS. The fixed rate never changes, but the inflation return rate is adjusted every six months and can also be negative (which of course brings your total return down).

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If interest rates rise, active fixed-income investors could invest in short-term bonds, which tend to remain fairly stable in rising rate environments, or use floating rate funds, which are more insulated from the negative impact of rising rates.

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