POOF! Our problems are gone

From "The Battle against Recession", the 22 April 1958 statement by Fed chairman William McChesney Martin:

The growth of business capital spending beginning in early 1955 was at a rate that was unsustainable. An economy with a long-run upward growth trend of about 3 or 4 per cent per year cannot sustain for long an increase in business investment of about 10 per cent per year ...

The Fed chairman seems almost careless, referencing "3 or 4 per cent" annual growth. He makes it sound like what, 3½ percent maybe? Pretty close to the 3.3% number that sticks in my mind. 

I took another look around the internet:

• A page at ResearchGate gives the average US Real GDP growth rate at 3.04% for 1960-2015.
  
  
• Google turns up this quote from TradingEconomics:

  GDP Annual Growth Rate in the United States averaged 3.09 percent from 1948 until 2021...

  but I don't find it at the link.

• YCharts has a "long term average" of 3.18% for the US Real GDP growth rate.
  
  
• I still remember Marcus Nunes, back in 2012, saying that
  

  It´s more or less recognized that US RGDP is trend stationary (maybe that´s changed now!), with real growth averaging about 3.3% from the early 50s to 2007.

These days it is difficult to find a long term average value for the real GDP growth rate, even on the internet. Maybe Marcus was right: The "trend stationary" concept has been purged from our thoughts. Or maybe it just got lost, like the Middle Ages was lost in the computer in the James Caan version of the Rollerball movie.

I think William McChesney Martin had a vested interest in making his listeners think growth was closer to 3% than 4%: He wanted to make the 10% growth rate of investment seem definitely unsustainable. Surely, 10% investment growth must be less sustainable if GDP growth is 3% than if it is 4% or more.

A 10% rate of investment growth is only about twice as much as 4% annual GDP growth. That isn't hopelessly unsustainable: Investment, after all, boosts the economy's ability to grow.

Statista shows total investment in China running between 30% and 40% of GDP -- easily twice the US GPDI -- between 1980 and 2020. Apparently that was sustainable.

"Average" growth is a number that applies to all the years you include in your calculation. Based on the average, the growth in any one year is just as good as the growth in any other. Based on the average for 1948-2021, for example, economic growth in 2020 was just as good as growth during President Reagan's "Morning in America", 1984.

It is more honest, a lot more honest, to consider the changes in the average as time goes by. For example, here's what I did find at TradingEconomics:

The United States is the world’s largest economy. Yet, in the last two decades, like in the case of many other developed nations, its growth rates have been decreasing. If in the 50’s and 60’s the average growth rate was above 4 percent, in the 70’s and 80’s dropped to around 3 percent. In the last ten years, the average rate has been below 2 percent...

On average, things are as good today as they ever were.