In a four-state survey, girls were found to be twice as likely as boys to be aggressive, and just as likely as boys to have problems with alcohol or drug use, findings that surprised psychologist Elizabeth Cauffman, who has worked for years with troubled teens in California and Pennsylvania.

The University of California at Irvine researchers gave psychological evaluations to more then 800 teens and then compared the results of teens in juvenile detention facilities to those who had never been incarcerated but shared similar backgrounds, race and socioeconomic status.

Psychologists know that in general, teen girls are more likely to internalize problems while boys act out through yelling or hitting, but Cauffman found that among incarcerated youths, teen girls are twice as likely as the boys to externalize their problems through aggression, according to the study published in the journal Youth Violence and Juvenile Justice.