Stockholm syndrome, or capture-bonding, is a psychological phenomenon in which hostages express empathy and sympathy and have positive feelings toward their captors, sometimes to the point of defending and identifying with the captors. These feelings are generally considered irrational in light of the danger or risk endured by the victims, who essentially mistake a lack of abuse from their captors for an act of kindness. The FBI's Hostage Barricade Database System shows that roughly eight percent of victims show evidence of Stockholm syndrome.Stockholm syndrome can be seen as a form of traumatic bonding, which does not necessarily require a hostage scenario, but which describes "strong emotional ties that develop between two persons where one person intermittently harasses, beats, threatens, abuses, or intimidates the other." One commonly used hypothesis to explain the effect of Stockholm syndrome is based on Freudian theory. It suggests that the bonding is the individual's response to trauma in becoming a victim. Identifying with the aggressor is one way that the ego defends itself. When a victim believes the same values as the aggressor, they cease to be perceived as a threat.