forceps delivery: delivery in which forceps are inserted through the vagina and used to grasp the head of the fetus and pull it through the birth canal; since the forceps can injure the fetus this procedure has generally given way to cesarean deliveries
psychological feature: a feature of the mental life of a living organism
spurious correlation: a correlation between two variables (e.g., between the number of electric motors in the home and grades at school) that does not result from any direct relation between them (buying electric motors will not raise grades) but from their relation to other variables