According to recent studies, those of us who grow up with at least one sister tend to be happier and more balanced than those who have only brothers. 

It is thought that girls get families talking, helping them to bond and encouraging members to reach their full potential.

Psychologists tested the emotional well-being of 571 people aged 17 to 25. Some had only sisters or brothers, some had both and others were only children. 

They found that those who had at least one sister were more optimistic, less stressed and better at coping with life's troubles. 

Researcher Tony Cassidy, of the University of Ulster, said: 'Our explanation for it is that the presence of girls opens up channels of communication and it becomes a much more expressive situation and that's positive. 

'Emotional expression is fundamental to good psychological health and having sisters promotes this in families.'

Those with sisters were also more ambitious, the British Psychological Society's annual conference heard.

Professor Cassidy said: 'It is about that intrinsic desire to want to do better every time, to strive towards goals. 

'It is something that underpins career development and success in all sorts of things. 

'It certainly seems there is something about the family situation with the number of girls in it that leads to more encouragement to achieve and be independent.' 

Both men and women benefited from having sisters. 

Men and women who grew up in broken homes benefited equally from the sister effect, but in stable homes, women got the most benefit. 

Brothers have a less positive effect, with the lowest scores overall being achieved by the men who had lots of brothers. 

Professor Cassidy said: 'The more natural trend for boys is not to talk about things. 

'When there are a number of boys together, it is almost like a conspiracy of silence not to talk, whereas a girl in that context breaks it down.' 

Children without siblings fared somewhere between those with only brothers and those with only sisters, possibly because they tend to build strong relationships outside the family. They tended to get the emotional support they needed elsewhere.