Now that Carlsen has decided not to defend his title the next official world champion will not be the world number 1. According to this tweet from Welsh GM Nigel Davies :

I would estimate that for something like 30-40% of the history of the World Chess Championship, the official champion has not been the World's strongest player. And in the grand scheme of things it's really not a big deal...

The PCA years when Kasparov was world number one but played his own world championship matches rather than the official ones is one time when this was true.

Nigel Davies estimate of 30-40% seems high to me. What is the real figure?