You might have heard the idea that being an only child means you're more likely to be selfish, spoilt, and self-centred – but the results of a new study show no link between being an only child and being more narcissistic.
It's an important finding for parents and policy makers alike – whether you're in charge of a single family unit or the strategy of an entire country.
Previous studies on the issue have been inconclusive, but the researchers behind the new analysis say it ticks all the boxes: a large sample, a representative sample, and built-in allowances for other variables (such as gender and socioeconomic status).
"Some of the past research has reported no difference between only children and non-only children in terms of narcissism and some of the past research has reported such a difference," says psychologist Michael Dufner, from the University of Leipzig in Germany.
"We can now say with rather high confidence that only children are not substantially more narcissistic than people with siblings."
Pulling data from a large longitudinal survey panel in Germany, the researchers analysed responses from 1,810 individuals, 233 of whom were only children, and 1,577 of whom had one or more siblings.
Parental socioeconomic status, gender, place of residence (urban or rural) and migration background were factored out of the responses – all these variables have been linked to influencing narcissism levels in the past.
The study looked at two personality traits in particular to measure narcissism: feelings of self-admiration and rivalry with others.
These traits were found to be no higher in people who grew up as an only child compared with people with siblings.
But it's probably going to take some time and effort to turn prejudices around.
In a separate experiment, the same scientists looked at questionnaires submitted by 556 people and found that many of us – with and without siblings – think that an only child is more likely to be narcissistic.
There are some caveats to mention. The study only looked at people in Germany, and only at two traits of narcissism – so we need to see the same results from other countries and across a broader range of personality traits to be certain about what we're seeing here.
However, it now looks likely that the commonly held assumption isn't true – and that has implications everywhere from the playground to the corridors of power. As always, it's best to stick to the science.
"When sociologists, economists, or policy makers discuss the downsides of low fertility rates, they should let go of the idea that growing up without siblings leads to increased narcissism," conclude the researchers in their published paper.
"There might of course be economic or societal costs associated with low birth rates, but increasing narcissism in the upcoming generation does not seem to be a factor that is relevant to the discussion."
The research has been published in Social Psychological and Personality Science.