From Cain and Abel and the Brothers Karamazov to Cinderella, the warmth and support provided by siblings is hardly taken for granted.
Now researchers have found that children who whine about their siblings may have good reason to complain: the more siblings teenagers have, the more it affects their happiness, they claim.
A study of secondary school children in the USA and China found that those from larger families had slightly poorer mental health than those from smaller families. The greatest impact was seen in families with multiple children born less than a year apart.
Doug Downey, a professor of sociology at Ohio State University, said previous work in the field has revealed a mixed picture of positives and negatives for children with more siblings, adding that the latest results “are not a given wasn’t”.
The researchers asked 9,100 eighth graders in the US and 9,400 in China, with an average age of 14, a series of questions about their mental health, although the specific questions differed between countries. In China, the teenagers without siblings did the best for mental health. In the US, children who had no siblings or only one were found to have similar mental health.
Overall, mental health was worse the more siblings the teens had, with greater impacts seen for teens with older siblings, and when siblings were closely separated in age.
Write in the Journal of Family IssuesDowney and his colleagues argue that the findings are consistent with the “resource dilution” explanation, the driving force behind the unwritten formula that states that the number of balls dropped rises, sometimes dramatically, with the number of siblings born.
“If you think of parenting resources like a pie, one child means they get all the pie,” Downey said. “But when you add more siblings, each child gets less resources and attention from the parents, and that can have an impact on their mental health.” That teenagers did worse when their siblings were a similar age supports the thinking, the researchers say.
But there are other possible explanations. For example, the teenagers with the best mental health come from families with the highest socio-economic advantages. In the US these were often families with only one or two children. In China it was the families with one child. In keeping with China’s one-child policy, about a third of Chinese children were only children, compared to 12.6% of American children.
With the rise of “one and done” families, researchers are increasingly keen to tease out the impact of siblings on mental health and other factors. Previous studies indicate a range of positive impacts linked to siblings, presenting a complex picture of advantages and disadvantages.
Earlier work by Downey showed that children with more siblings got along better with others at preschooland was less likely to divorce in later life – perhaps because they already had some experience navigating close relationships. Meanwhile, a 2016 study of more than 100,000 Norwegian children found better mental health in larger families over the centuries.
