Right now there are about ~7.6 billion people alive.

In total there have been approx. ~108 billion people.

Assuming ghosts exist, and when a ghost dies it becomes a ghost-ghost,
we can assume this 7% fraction exists for each remaining group of souls.

Thus, here's a population count for each level:

Seems very lonely for these last few ghosts...

A spooky halloween lesson by @rtaylz