I HOPE to write more about some of the labour-market sessions I attended in Chicago; the effort continues to slice and dice recent data in an effort to understand the nature of America's current employment problems. I think there is a misguided tendency to declare the American job market afflicted by just one problem or another; either current problems are cyclical or their structural, for instance. In fact, America's employment shortfall is very well explained by its growth shortfall. Now, it's possible that structural unemployment problems are constraining growth, though this is more difficult to show than you might think. But growth, when it occurs, seems to be generating employment more or less as we'd expect.

Beneath these macro dynamics, however, there are lots of interesting things going on, some of which are a part of long-term trends. I'll just give you one quick example, which sheds some interesting light on the December employment report that came out on Friday.

The American workforce, by many accounts, has been polarising. Middle-skill jobs in manufacturing and many business services have been disappearing thanks to automation and international competition, but low- and high-skill employment is increasing. During the recession and recovery, this dynamic has become somewhat skewed. Highly skilled workers have done best, low-skill workers have done poorly, and those in middle-skill employment have done very, very poorly, even as the job market has improved over the past year. So, in the year to December, employment among workers without a high-school degree rose by 126,000. Employment for workers with a college degree rose by just over 1m jobs. For those with just a high-school diploma, however, employment fell by 551,000.

Meanwhile, employment for workers without a diploma is about 1.3m jobs short of the pre-recession level, and it's about 3.2m jobs short of the pre-recession level for workers with high-school credentials. There are 1.7m more college-educated workers on the job now than was true in late 2007, however.

Part of this may be that workers will lower skill levels are concentrated in many cyclically variable industries, like construction. A deep recession and slow recovery will inevitably be relatively easier on those with higher skill levels, in that case. But recent recession-oriented changes have probably also accelerated underlying structural shifts, leaving times good now for those who'd already had a pretty nice decade or so before the crash.