Many blended families get along better than traditional nuclear families and have deep, lasting relationships even if some of them aren’t blood-related. According to statistics, however, blended families are more prone to hardships and struggles than a traditional family, and most of the struggles seem to be centered on the children.

Using collected data from the National Longitudinal Study of Youth, researchers from Bowling Green State University and Iowa State University found that adolescents with half-siblings born from a different father were more likely to have sex before the age of 15 and also do drugs. The act of having children with multiple partners is called "multi-partnered fertility" and according to Karen Benjamin Guzzo, an assistant professor of sociology at Bowling Green State University, "It's not new behavior, but it's happening more often as more people are having children outside of marriage.”

The new study is one of the first conducted that examines the effect of parental MPF on children over a long period of time, and it’s also the only study that inspects background factors like the mother’s education history, household poverty, and the number of changes in the family structure that the adolescent has experienced.

After looking at this data, researchers examined the relationships between maternal re-partnering and additional childbearing and the adolescent use of drugs and early sex.

Guzzo explains that "for children, MPF means having a half-sibling, but it also means, for first-born children, that they usually experienced their biological parents splitting up -- if they were together at all, lived in a single mother household for some time, experienced their mother finding a new partner at least once and perhaps lived with a stepfather, and finally experienced their mother having a baby with a new partner.”

According to the research, adolescents with half-siblings are about 65% more likely than adolescents with full siblings to use drugs such as marijuana, cocaine, sedatives, uppers, crack, inhalants, and other drugs by the time they turn 15. In addition to this, they are about 2.5% more likely to have sex before the age of 15 as well.

Guzzo says that it’s not yet clear what causes these outcomes, but that the research team plans to examine the reasons more in-depth in the future and explore differences in maternal behaviors, father and stepfather involvement, and adolescent observations of their relationship with their mother to discern if these dynamics explain the association between having half-siblings with a different father and unsafe adolescent behavior.

Source: American Sociological Association (ASA) (2013, August 11). Research shows negative effects of half-siblings. ScienceDaily.