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

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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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Although the investments resembled bonds, paying buyers a fixed interest rate for taking on the default risk of corporate debt, the products invested in synthetic collateralized debt obligations held by Lehman.

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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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The fact that early bonds had no fixed maturity date ensured that any change in interest rate was fully reflected in the capital value of the bond.

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