In astronomy I've always heard the rule of 10s. 10% of astronomers get the PhD, 10% of the PhDs get post docs, 10% of post docs get tenure. And tenure in 0-2

In astronomy I've always heard the rule of 10s. 10% of astronomers get the PhD, 10% of the PhDs get post docs, 10% of post docs get tenure. And tenure in 0-2 years? That's impossible outside of China or India or the Soviet bloc. I think the average amount of time an Astronomer spends in post-docs is 9-12 years.