The third possible explanation is that the gap between job advertising and new hires reflects the growing use of companies' "internal" labor markets. A variety of other indicators - including fewer people moving to take new jobs - suggests that companies are often filling openings from within.
Many nonetheless advertise such positions externally, which would boost the job-offer rate in the data. The survey counts only jobs filled from outside a company in its statistics on hiring, so the increase in job-offer rates for this reason would not correspond to an increase in hiring rates.
This possibility doesn't explain why the gap is wider for smaller businesses, because larger companies have more robust internal labor markets. But it is consistent with anecdotal evidence that external applicants are facing more onerous interview processes and that companies are hiring outside job candidates only slowly and cautiously.
A related interpretation, favored by Steven Davis of the University of Chicago, Jason Faberman of the Federal Reserve Bank of Chicago and John Haltiwanger of the University of Maryland, is that companies have reduced their "recruiting intensity." They advertise jobs but don't have much interest in filling them.
These possible explanations for the openings-hiring gap have substantially different implications. The mismatch theory, which seems the least plausible of the three, is the most depressing, because it implies we're in for more painful adjustment and sluggish job growth.
The Krueger theory suggests that as companies adjust their wage offers to an improving labor market, the gap will narrow. And the notion that internal hiring and recruiting intensity explain things implies that the gap itself is a bit of a mirage.
Regardless of the true explanation, it's still good news that more jobs are being advertised. That wouldn't be happening if the economic outlook were entirely bleak.
Peter Orszag is chairman of the financial strategy and solutions group at Citigroup and a former director of the Office of Management and Budget in the Obama administration. This column was distributed by Bloomberg News.