1. Do the math. If the GNP/economy/whatever is being measured grows 10% each year, how long before the GNPetc becomes 200% of that in 1980? It has therefore doubled. (This would have happened in about 1988 if growth is compounded.).
And between 1980 and when this article was written, this happened three times - the economy doubled, three times.
2. He is referring back to either some earlier chapter of his (if this is a book), or some other book that he has mentioned earlier in the article or book.
Student or Learner