There’s a fun article in the FT today about the practice of extrapolating from current trends. Unless you are a subscriber, you’ll only get the first couple of paragraphs, but you’ll see the general idea:
At the time Elvis Presley died in 1977, he had 150 impersonators in the US. Now, according to calculations I spotted in a Sunday newspaper colour supplement recently, there are 85,000. Intriguingly, that means one in every 3,400 Americans is an Elvis impersonator. More disturbingly, if Elvis impersonators continue multiplying at the same rate, they will account for a third of the world’s population by 2019.