Mahalanobis quotes Peter C.B. Phillips and Donggyu Sul,

the fastest learning countries are China, India and the East Asian group. Remarkably, China has experienced over four centuries of base trajectory OECD growth in the last 52 years taking it to year 1917 levels on the OECD trajectory. India and the East Asian group of countries have experienced more than three and a half centuries of base trajectory growth in 52 years, taking them to mid-nineteenth century OECD levels of income.

It took me a few moments to understand what the authors were doing, but it is an interesting metric. They take each region of the world and look at per capita income 52 years ago. They then match this up with the year that the OECD reached that level of income. This gives the “OECD year” the other region started from. Then they look at the region’s most recent per capita income and figure out its “OECD” year. That way, you measure the region’s economic growth in OECD years.