If you rank the countries of the world in terms of the academic performance of their schoolchildren, the U.S. is just below average, half a standard deviation below a clump of relatively high-performing countries like Canada and Belgium.

NEWYORKER: Most Likely to Succeed

Once you know the average return, the standard deviation of each index and the correlation coefficient between each pair of indexes, the rest is math.

FORBES: Asset Allocation and the Efficient Frontier

The gray area around the average line shows the two standard deviation range of the data.

FORBES: U.S. Navy Scrambles for Piece of Arctic Pie