I recently led a research team to the Rio Grande Valley in Texas, where Gov. Rick Perry, a contender for the Republican presidential nomination, has advertised his track record of creating jobs. From January 2000 to January 2010, employment in the Valley grew by a remarkable 42 percent, compared with our nation’s anemic 1 percent job growth.

But the median wage for adults in the Valley between 2005 and 2008 was a stunningly low $8.14 an hour (in 2008 dollars). One in four employed adults earned less than $6.19 an hour. The Federal Reserve Bank of Dallas reported that the per capita income in the two metropolitan statistical areas spanning the Valley ranked lowest and second lowest in the nation.

These workers aren’t alone. Last year, one in five American adults worked in jobs that paid poverty-level wages. Worker displacement contributes to the problem. People who are laid off from previously stable employment, if they are lucky enough to find work, take a median wage hit of over 20 percent, which can persist for decades.