A new study finds that quarreling siblings increase stress for the children as well as the parents.

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onventional wisdom holds that children without brothers and sisters are maladjusted and lonely compared to those with siblings. Not so, says a new British study from the University of Essex, which suggests that only children may have a better chance of happiness. Here's a concise guide:

What did the study find?
Only children are happier than those with siblings, which may reflect the fact that they endure less bullying — something more than half of kids with siblings in the study reported. "Quarreling siblings increase stress for parents and some [parents] just give up intervening or intervene inconsistently, leaving the field wide open for the bully sibling," says one researcher.

How was the study conducted?
The study questioned 2,500 young people as part of a larger initiative called Understanding Society that is tracking 100,000 people in 40,000 homes in the United Kingdom, where 46 percent of families are only-child families.

How do these findings compare with other recent studies?
It contradicts them. A 2004 Ohio University Study found that only children had a harder time making friends when they start kindergarten compared to kids with siblings. Other recent studies have found that those with sisters, both children and adults, tend to be happier and more optimistic.

Who are some notable only children?
Chelsea Clinton, Robin Williams, Tiger Woods, Sarah Michelle Gellar, Alicia Keys, and Natalie Portman are all only children. Portman says being sibling-free made her who she is: "I would never have been an actress if I weren't an only child, because my parents would never have let me be the star of the family at the expense of another child."

Sources: The Telegraph, Daily Mail, CapitalBay.com, Metro UK, Top News, The New York Times