The combination of a zero interest rates policy and quantitative easing is what has pushed government bond yields to historical lows.

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If successful, bond yields will rise and all you need is 2% bond yields for interest costs to eat up 80% of Japanese government revenues.

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When thinking about the cost of this kind of arrangement, many people would focus on the interest rate on the bond the government is issuing (just as they focus now on the interest rate on the promissory notes).

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That points to an extra one percentage point on interest rates for the higher risk that comes with being small and in an illiquid part of the government bond market.

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Interest on those bonds are paid back to the bond holders through the unlimited taxing powers of the US government, which is what makes them AAA rated.

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Italy's government paid an interest rate of 6.47% to borrow 3bn euros for five years at a bond auction, up from 6.3% last month.

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They found that it made sense to buy long bonds in almost all interest-rate scenarios but one: when rates are low (so the risk that they will revert to the mean, thus undercutting the value of the bond, is high) and the yield curve a line drawn through the interest rates on government securities with different maturities is flat (so there is little extra reward for taking that risk).

ECONOMIST: Buttonwood