"We don't have a complete answer, but economists think a lot today has to do with technology," says Walden, a specialist with the North Carolina Cooperative Extension Service.

"Computers for example: Computers now can do things that are routine -- anything that follows a rule. And what this has done is it has freed up more people to focus on more complex tasks -- tasks that require reasoning, analysis and decision making. And quite frankly you need an education for that.

"Take one example -- take the auto mechanic business," he adds. "In the old days someone would learn to be an auto mechanic by maybe tinkering around on the farm or in their garage. Today auto mechanics have to be well trained: They go to school. They go to workshops. They have to read manuals. They have to read computer analyses.

"So all that requires education, knowledge," he concludes. "And ... that viewpoint is pervasive throughout our economy."