In the first half of 2009, three-fourths of tracker countries saw GDP shrink ... rate and estimated potential growth rate over time. The top chart shows these two data series plotted together.

President Donald Trump predicted that GDP could expand as much as 9% a year, compared with Congressional Budget Office projections for an average of 1.8% growth each year for the next decade.

However, the compound annual growth rate (CAGR) of GDP over time is a far more important indicator. A high GDP CAGR suggests that an economy is developing not just consistently, but also ...