Various studies of the effects neutering has overall on male and female dog aggression have been unable to arrive at a consensus. A possible reason for this according to two studies is changes to other factors have more of an effect than neutering.   One study reported results of aggression towards familiar and strange people and other dogs reduced between 10 and 60 percent of cases,  while other studies reported increases in possessive aggression  and aggression towards familiar and strange people,  and more studies reported there was no significant difference in aggression risk between neutered and non-neutered males.   For females with existing aggression, many studies reported increases in aggressive behavior     and some found increased separation anxiety behavior.   A report from the American Kennel Club Canine Health Foundation reported significantly more behavioral problems in castrated dogs. The most commonly observed behavioral problem in spayed females was fearful behavior and the most common problem in males was aggression.  Early age gonadectomy is associated with an increased incidence of noise phobias and undesirable sexual behaviors [ clarify ] .