I have a goal to ressurect x ghosts in y region. I usually do this, by killing my adults in various ways, because i have the feeling, that some of them don't return as ghosts.
For example: Throwing villagers in a cullis gate, seems to prevent them from becoming ghosts. Is that true?
Also killing them far away from your village, like dropping them in front of a enemy tower on corrupted land, does not produce ghosts, right?
Setting them on fire, or freezing them to death in your village, seems to work best, except for starving them all, but that can get out of control quickly :-)
Another thing: In full moon nights is a higher chance to discover ghosts, isn't it?