Its called a liquidity premium and its variance over time drives both difference in volatility and average return between investment vehicles.

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Cost of carry on my bond portfolio of high yield paper is also minimal, but shows a net positive variance of over 500 basis points.

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Mr Sides's findings may also reflect a phenomenon identified by Moody's Analytics: over time, states' economic performance has converged, and the variance between their growth rates now matches the lowest in 70 years.

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The variance on either side of neutral ranges as high as 15 to 20 percent over the next 12 months.

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