From the mid-17th century to the late 20th century, the American economy grew roughly 3.5% a year. That growth rate has since declined significantly. When the final figures are in for 2012, the annual rate of real output growth for the first dozen years of this century is likely to be about 1.81%.

What accounts for the slowdown? An important part of the answer is simple: Americans aren't working as much today. And this trend reflects more than the recession and sluggish economy of the past few years.

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