Many parents ponder why one of their children seems more emotionally troubled than the others. A new study in the United Kingdom reveals a possible basis for those differences.

Adolescents who view their households as more unstructured, disorganized, or hectic than their siblings develop more mental health and behavioral problems in early adulthood, according to the study. The findings are published in Psychological Science, a journal of the Association for Psychological Science.

In research tracking thousands of twins born in the mid-1990s, Sophie von Stumm, a psychology professor at the University of York, found that teenagers who perceived their homes as more disorganized, unstructured, or fast-paced than their siblings suffered more anxiety and depression and engaged in more substance use and problem behavior. If future research confirms those findings, she said, psychologists could develop interventions that modify adolescents' perceptions of their home environments.

von Stumm said she's long been curious about why people who share an experience come away with vastly different perceptions and interpretations of what happened. For her study, she used data from 4,732 same-sex twin pairs from the Twins Early Development Study (TEDS), an ongoing examination of twins born in the mid-1990s in England and Wales. She excluded data from opposite-sex twin pairs to rule out potential gender-based differences in perceptions.

At ages 9, 12, 14, and 16, the twins and their parents rated the level of routine, noise, and general confusion in the home.

"Some households are more chaotic than others: There's always a TV or radio playing, different people come and go every day, and there are no routines, like regular bedtimes or mealtimes," von Stumm explained.

In reviewing responses from the twins at age 16, she observed that siblings could have significantly different views about the atmosphere in their home. One sibling might view the household as far more noisy and fast-paced than the other.

"You'd think the siblings grew up in different families," von Stumm said. "That's how subjective their perceptions are."

At age 23, the twins completed a questionnaire designed to measure their educational attainment, employment status, income, substance use, sexual risk-taking, conflicts with the law, mental health, and behavioral tendencies. Those who had, at age 16, reported experiencing greater household chaos than their twin siblings scored higher on depression, anxiety, antisocial behavior, and other mental health problems. The results were consistent across both identical and fraternal twin pairs.

"Siblings who perceived the household as more chaotic than their brothers or sisters reported poorer mental health outcomes in young adulthood," von Stumm said. "This association was evident from adolescence onwards, confirming theories that the onset of mental health issues likely is during teenage years."

von Stumm said she next plans to explore the precise age and reasons that siblings start to differ in their perceptions of household chaos.

"It is possible that children who experience more adverse events in early life than their siblings, like suffering an injury or being excluded from school, develop a heightened sensitivity to household chaos that then has long-term effects on their mental health," she said. "Because many common adverse early-life events, such as parental conflict or separation, affect all children of a family, we don't know yet if there are specific ones that can cause poor long-term mental health."