‘The average necromancer is haunted by 10 ghosts’ factoid is a statistical error. The average necromancer is haunted by 0.5 ghosts.
Harrowhark The First (whilom Nonagesimus), the Ninth Saint to serve the King Undying, who created a bubble in the River and is haunted by 200 dead children, the corpse of the Locked Tomb, her dead cavalier, the dead mom of said cavalier, the people who died back at Canaan House and her former cavalier who died in an exploding shuttle is an outlier and should not have been counted.