Why your sister and mum don't like your boyfriend

The research, undertaken by the Norwegian University of Science and Technology (NTNU), shows the reason your boyfriend's mother-in-law doesn't like you probably isn't down to your awkwardness or bad jokes -- but more likely a result of something called the 'Juliet Effect'.

The 'Juliet Effect' is a phenomenon by which parents are opposed to the romantic relationship of their child - and the researchers theorise that this comes about because the criteria for a good partner varies wildly between parents and their children.

The name comes from the Shakespearean play Romeo and Juliet, two teenage lovers whose families were in a constant feud.

Juliet’s mother would rather see her daughter marry Paris,plain but rich, than heartthrob Romeo.

The idea is based on something likely familiar to women over the world – you bring home a good looking guy to meet the family, but his finances are not so secure. He may be the nicest guy in the world, but your mum and sister think you should go for someone plainer, who has a secure financial future.

While it appears those female relatives only have your best interests at heart, the study casts doubt on their motivations.

It finds when it comes to genetics, it pays for mothers and sisters to be cautious because a financially-unstable suitor is unlikely to be able to offer long term support or prestige for the family.

However for the woman actually in this relationship it pays genetically to choose the good looking lover, as it means she is likely to have more healthy attractive children, who have a greater chance of finding partners of their own, thus ensuring her genes are passed on.

While this has been already studied between mothers and daughters, the link to the sisters is new.

Dr Robert Biegler, Associate Professor from the Norwegian University of Science and Technology's Department of Psychology said sisters also prioritise qualities in their sister's partner that can provide direct benefits for the whole family, the UK Telegraph reported.

To find out whether sisters would pick the same type of partner for themselves as for their siblings, the researchers asked 133 pairs to describe their perfect other-half and who they would choose for their sister.

"For the most part, women choose the same ideal partner characteristics for themselves as for their sister,” added Dr Biegler.

“But the women perceived characteristics like being understanding, empathetic, responsible, helpful, sensible and kind as more important for their sister's partner than for their own.”

Women found being sincere, humorous, charming, sexually satisfying and fun as more important for their own partner than their sister's.

The reason is to do with genetics, the study finds women prefer for their daughter or sister to choose someone who can contribute to the upbringing of their own children and grandchildren, who are not a burden to the family.