Shared interests will often cement a relationship, as do shared values and opinions. Some couples seem made for each other – but there's an awful lot of couples that leave you wondering how they got together in the first place.

He votes Republican, she doesn’t vote at all. She loves cats, he's allergic to them. He's a party animal, shed rather stay at home with a good book. You know these couples – they're everywhere. But what does the research say?

An article by David Partenheimer on the American Psychological Association's website outlines a comprehensive couples study by the University of Iowa. Psychologist Eva C. Klohnen, along with graduate student Shanhong Luo, looked at 291 newlywed couples to study "assortative mating issues" – which is coupling "based on similar or opposite characteristics".

The study revealed that the couples had "highly similar" values and attitudes but "they possessed little or no above-chance similarity on personality-associated areas such as attachment, extraversion, mindfulness and positive or negative emotions. There is no scientific proof that opposites do in fact attract. What is most fascinating is that when the investigators evaluated matrimonial quality and happiness, they determined that personality resemblance was associated with marital gratification, but attitude similarity wasn't".

Science tells us that we're unconsciously attracted to people who have a different genetic pattern – a different immune system – to our own, and that this makes for the best chance of producing healthy offspring (science always reduces romantic love to mere biology!). But immune systems and life values are two very different things.

Another American study published in the Proceedings of the National Academy of Sciences in 2003, came to similar conclusions as the Iowa research: "in Western civilization, humans do not use an “opposites-attract” or a “reproductive-potentials-attract” determination in their selection of long-term mates but rather a “likes-attract” pattern founded on a preference for partners who are alike to their own personalities across a number of characteristics".

Dr Neil Clark Warren, author of the book Date Or Soul Mate? How To Know If Someone Is Worth Pursuing in Two Dates Or Less, believes that opposites often attract, but they can drive each other mad. Warren has counseled married couples for 30 years and one of the cornerstones of his philosophy is "finding someone similar to you".

Romance, though, rarely plays by the scientific or psychological rules, so if you find yourself in a relationship with someone that you probably wouldn't even be friends with, take stock of what common ground you do have – if there is any! – and learn to respect each other's differences.

Also learn from other people's relationships. Many of us have friends or family that are in relationships where personalities clash and don't compliment one another. Allow your partner to be themselves, trying to change their behaviour will never work and will only add resentment to the relationship.

Avoid heated debates on, for example, politics. Agree to disagree and see what you can learn from each other. If things get heated, give your relationship the priority – your romance is more important than being right or having the last word.