Attempts to define and describe violence and abuse in hetero-normative intimate relationships can become contentious as different studies present different conclusions about whether men or women are the primary instigators. For instance, a 2005 study by Hamel reports that "men and women physically and emotionally abuse each other at equal rates." Basile found that psychological aggression was effectively bidirectional in cases where heterosexual and homosexual couples went to court for domestic disturbances. A 2007 study of Spanish college students aged 18–27 found that psychological aggression (as measured by the Conflict Tactics Scale) is so pervasive in dating relationships that it can be regarded as a normalized element of dating, and that women are substantially more likely to exhibit psychological aggression. Similar findings have been reported in other studies. Strauss et al. found that female intimate partners in heterosexual relationships were more likely than males to use psychological aggression, including threats to hit or throw an object. A study of young adults by Giordano et al. found that females in intimate heterosexual relationships were more likely than males to threaten to use a knife or gun against their partner. However, studies that allege that women use violence in intimate relationships as often or more often than men are incomplete and fail to consider the reason or goal of the violence. In intimate relationships, women's violence is most often self-defense, while men's violence is most often part of an ongoing effort to control and dominate the woman partner.