The aim of horror in cinemas is to play to masochistic (pleasure in inflicting pain) fears. Masochism always dominated over sadism (pleasure in having pain).
Killers either have childhood issues or are sexually disturbed. Female killers have gender confusion, or other problems.
Horror tends to happen in decaying/ haunted houses. The back stories of these places can be terrible, due to a disturbing history. Also walls in houses can make the victim feel safe... until the killer starts to hack in to them.
NO GUNS. If there are firearms, then they tend not to work, like the phone.
Victims tend to be young beautiful women that have had sexual experiences.
The final girl theory. That the only girls that tends to live are, intelligent, boyish, a virgin and has a name that is boyish.
Slashers are implied at males. This is because they will cheer on the killer, and then be sympathetic towards the victim.