The most efficient investments are those such that no other investment has a higher return for the same amount of standard deviation.

FORBES: The Efficient Frontier

The 20% rate thus is defined as a deviation, an "expenditure" in the amount of up to 19.6%.

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The standard deviation formula goes like this: 1.1 x the amount bet x the square root of the number of hands played.

FORBES: High Frequency Trading And Blackjack

The table includes an annualized return, annual standard deviation of the technique, best and worst calendar year return, and the high and low amount in equity over the period.

FORBES: Choices in Portfolio Rebalancing