Research from De Montfont University and Ulster University claims that having a sister makes you happier and more optimistic.
The study surveyed 571 people aged 17 to 25 on their lives and found that those who grew up with sisters were more likely to be happy.
Participants filled in psychological questionnaires that were used to assess a range of issues, including mental health and a positive outlook.
It turns out sisters encourage their siblings to be more open and communicative about their feelings, which promotes good mental health.
However, brothers seem to have the alternative effect. It could be that boys have a natural tendency not to talk about things and girls tend to break that down.