When a father is not present in the home, his son is twice as likely to end up in jail, according to a new study by Cynthia Harper of the University of Pennsylvania and Sara S. McLanahan of Princeton University.

Tracking a sample of 6,000 males ages 14 to 22 from 1979 to 1993, the sociologists also found that even after accounting for differences due to race, income and education:

• Those boys who grow up with a stepfather in the home were even more at risk than those with an absent father, with a roughly three times greater risk of incarceration than those who reside with both their parents.

• Young men whose parents part ways during their adolescence were roughly one and a half times as likely to wind up in jail as children from intact families -- faring slightly better than boys who were born to single mothers.

• While whites have lower rates of father absenteeism than blacks, white youths whose families split are at a higher risk of incarceration than their black peers.

• The presence of live-in grandparents in households without fathers "appears to help improve youths' chances of avoiding incarceration," the study found.