In Grantham's opinion, the U.S. trend GDP growth rate has fallen from over 3% a year to at best 1.5%.

This is an opinion, so judge whether the measurable parts it rests on hold as of 2020. Part (a): the long-run U.S. trend in real GDP growth was historically over 3% a year (for example, the post-war average to about 2000). Part (b): credible measures of U.S. trend growth around 2020 were at or below about 1.5% a year. Valid measures are CBO potential-growth estimates, the Fed's long-run growth projection, or trailing 10-year average real GDP growth. True: (a) holds and the measures for (b) sit at or below about 1.6%. Mostly true: (a) holds and the measures sit at about 1.6% to 2.0%, below 3% but slightly above Grantham's 'at best' figure. Mixed: (a) holds but the measures are clearly above 2.0% and below 2.5%, or (a) is weak (about 2.5% to 3%) while (b) holds. Mostly false: the measures are about 2.5% or higher, or the historical trend was clearly below 3%, but some decline from the past is still visible. False: the historical trend was not over 3% and the 2020 measures show no meaningful decline.

Set before the research began.

1. E1 Economic Growth - HumbleDollar HumbleDollar (Jonathan Clements LLC)

   “REAL GROSS DOMESTIC—meaning growth adjusted for inflation—climbed 3.6% a year over the 50 years through early 2000, according to data from the U.S. Department of Commerce’s Bureau of Economic Analysis.”

2. E2 Is Slow Still the New Normal for GDP Growth? Federal Reserve Bank of San Francisco (FRBSF Economic Letter 2019-17) · 24 June 2019

   “Estimates suggest the new normal pace for U.S. GDP growth remains between 1½% and 1¾%, noticeably slower than the typical pace since World War II.”

3. E3 Is Slow Still the New Normal for GDP Growth? Federal Reserve Bank of San Francisco (FRBSF Economic Letter 2019-17) · 24 June 2019

   “Combining that with the CBO’s projected growth in hours of 0.5% per year results in our preferred modal estimate for GDP growth of 1.6% per year.”

4. E4 Assessing Global Potential Output Growth: October 2020 Bank of Canada (Staff Discussion Paper 2020-10) · October 2020

   “After accounting for the four channels described above and other factors, such as population aging and structurally low productivity, staff estimate that US potential output growth will decrease from 1.8 percent in 2019 to 1.1 percent in 2020 (Chart 2).”

Part (a) holds: E1, citing BEA data, reports 3.6% a year real GDP growth over the 50 years through early 2000. For part (b), the San Francisco Fed put the "new normal" U.S. growth pace at 1½% to 1¾%, with a modal estimate of 1.6% (E2, E3). The Bank of Canada estimated U.S. potential output growth at 1.8% in 2019, falling to 1.1% in 2020 (E4). Together these estimates range from 1.1% (2020) to 1.8% (2019), with the San Francisco Fed putting the new normal at 1.5–1.75% and its modal estimate at 1.6% (E2, E3), close to Grantham's 'at best' 1.5% figure and well below the historical trend of over 3% (E1). None of them is exactly one of the measures the criteria name (CBO potential growth, the Fed's long-run projection, or 10-year average growth), but they are comparable trend-growth estimates.