For two decades the EU has grown more slowly than the United States and far more slowly than China and India. The gap shows up in a few places.
Real GDP growth. Year after year, US growth has tended to outpace the eurozone's, and emerging Asia has grown faster still.
GDP per capita. Income per head is the cleanest measure of prosperity. The gap between the average American and the average EU citizen has widened over time.
Compounding. A persistent one- or two-point difference in annual growth becomes an enormous difference in living standards over a generation.
The caveats
Cross-country comparison is harder than it looks: exchange rates, price levels and how output is measured all affect the picture, and the EU scores well on other measures such as inequality and life expectancy. The region-comparison charts on the euro page use IMF data on a consistent basis so the trend is read fairly.