Second, if house lock were an important factor, we would expect to see greater declines in labor mobility in states with more underwater mortgages, and among homeowners compared with renters. A study scheduled for publication in The Journal of Economic Perspectives finds no support for either of these hypotheses.

Narayana Kocherlakota, the president of the Federal Reserve Bank of Minneapolis, made waves last August when he pointed to a recent climb in posted job vacancies as evidence that current unemployment is mainly structural. Normally, there wouldn’t be this many vacancies until unemployment were closer to normal. Therefore, he argued, a severe mismatch between unemployed workers and the skill requirements or location of available jobs had raised the normal unemployment rate by as much as three percentage points.

But this analysis misses the fact that early in recoveries, vacancies typically rise relative to unemployment. Also, as discussed by Peter A. Diamond in his recent Nobel prize lecture, businesses that are relatively more plentiful today — for example, larger companies and those outside of construction — tend to post their vacancies more consistently. Thus, the changing composition of companies helps explain the unusual rise in vacancies.

When experts weigh the evidence, they come down strongly on the side that normal unemployment has not risen greatly. Once a year, the Survey of Professional Forecasters asks respondents for their estimate of the natural unemployment rate. In the third quarter of 2010, the median estimate was 5.78 percent, almost exactly one percentage point higher than in the third quarter of 2007, just before the recession started. (The highest estimate was 6.8 percent.) And the Congressional Budget Office uses 5.2 percent as its estimate of the natural rate.

All of this suggests that most of our high unemployment is still the consequence of low demand. Consumers remain hesitant to spend because unemployment and debt are high. Companies are unwilling or unable to invest because customers are few and credit is still tight.

This diagnosis suggests that the appropriate remedy is to stimulate demand. In February, I suggested a number of steps the Federal Reserve could take. Some additional fiscal measures would also be useful. More public investment (as the president has advocated), additional aid to state and local governments, and a cut in payroll taxes for employers would all help. Given the severity of the long-run budget problem, short-run fiscal stimulus should only be undertaken as part of a comprehensive package of gradual spending cuts and tax increases. That would give the economy the jolt it needs, while providing reassurance that the United States will remain solvent over the long haul.