Only Germany is wealthier than it was in the first quarter of 2008, when economic activity peaked. France is close, according to Mr. Rupert and Mr. Cooley, a professor at the Leonard N. Stern School of Business at New York University. (The two publish a blog that tracks the business cycle, at european snapshot.com.)

Spain and Italy are both effectively back where they were in the darkest days of 2009, after the collapse of Lehman Brothers set off a financial crisis that undermined the world economy.

Both countries resumed growing in 2009, but stalled in the middle of last year. Since then Spain has had three quarters in a row of declining gross domestic product, while the Italian economy has been shrinking for a year. There is little doubt they are deep in recession. Some economists predict that France and even Germany could follow.

In contrast, the United States regained all the ground lost since 2008 at the end of 2011. But it took twice as long to do so than had been the case for any other recession since World War II, according to Mr. Cooley and Mr. Rupert. They estimate that, had the United States continued growing at the same average pace as it has since 1950, the country would be more than $1.5 trillion wealthier today.

While economists already knew that euro zone G.D.P. was still catching up with 2008, experts like Mr. Cooley and Mr. Rupert have been parsing the sometimes inconsistent statistics issued by European countries to show how broadly the downturn has affected Europe’s largest economies in the form of rising unemployment, declining consumer spending and falling investment.

Mr. Weinberg and others warn that the euro zone is on the same path as Japan was in the 1990s, when failure to deal with weak banks led to a decade of stagnation.