A favorite "progressive" trope is that America's middle class has stagnated economically since the 1970s. One version of this claim, made by Robert Reich, President Clinton's labor secretary, is typical: "After three decades of flat wages during which almost all the gains of growth have gone to the very top," he wrote in 2010, "the middle class no longer has the buying power to keep the economy going."

This trope is spectacularly wrong.

It is true enough that, when adjusted for inflation using the Consumer Price Index, the average hourly wage of nonsupervisory workers in America has remained about the same. But not just for three decades. The average hourly wage in real dollars has remained largely unchanged from at least 1964—when the Bureau of Labor Statistics (BLS) started reporting it.

Moreover, there are several problems with this measurement of wages. First, the CPI overestimates inflation by underestimating the value of improvements in product quality and variety. Would you prefer 1980 medical care at 1980 prices, or 2013 care at 2013 prices? Most of us wouldn't hesitate to choose the latter.

Second, this wage figure ignores the rise over the past few decades in the portion of worker pay taken as (nontaxable) fringe benefits. This is no small matter—health benefits, pensions, paid leave and the rest now amount to an average of almost 31% of total compensation for all civilian workers according to the BLS.