Image: Before Sunrise.

Fact: relationships are complex.

From the outset, there’s no telling whether two people can stay together for the long haul — or even make it through a first date. But that hasn’t stopped researchers from trying to determine why some relationships work better than others; they’ve been chipping away at that for years.

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Just this week we’ve stumbled on two findings that could come in handy for anyone who’s currently in a relationship — or who is currently navigating the murky waters of dating.

The science of a great first date.

A study by researchers at two American universities has investigated why some couples just 'click' on a first date, and much of it comes down to conversation. Evidently, men and women engage more strongly with different speech patterns and habits.

As The Washington Post reports, women felt most connected when their dates 'mimicked' their laughter (i.e. laughed right after they did); 'interrupted' them to ask questions that showed they were interested; said things that indicated appreciation; and used the word "you". (Post continues after gallery.)

Men were most engaged when their dates spoke about themselves using words like "I" and "me", and the researchers suggest if a woman asked a man a lot of questions about himself, she was possibly doing it to save a lagging conversation. Which kind of goes against everything we've ever been told about dating — namely "Rule 1: Ask all the questions."

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On the other hand, men felt less connected when their dates "hedged", meaning they punctuated their speech with terms like "I guess", "sorta" and "probably".

So how the hell do you figure out if you date is feeling this mythical 'click'? Apparently, there are some verbal cues to listen out for.

When a woman is feeling connected, apparently she'll speak at a higher pitch, vary her volume and use self-markers; and she'll comfortable speaking about herself (using the word "I") rather than asking a lot of questions.

On the other hand, men show this connection by laughing and varying their volume, but the pitch they speak at won't change.

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This is all very interesting, but if a first date has been successful you'll probably be able to tell without listening intently to the pitch of your love interest's voice. So probably just carry on enjoying your gelato and being your witty, wonderful self. (Post continues after gallery.)

The science of a happy relationship.

It's one thing to get through a first date — and all the dates that follow — but maintaining a happy, healthy relationship can be challenging to say the least. The website Happify has collected data from scientific studies into what makes for a strong romantic partnership, and there are some useful takeaways.

Firstly, it seems 'happy' couples talk more, and have five positive interactions for each negative one. Positive interactions refer to actions like giving a compliment, or reliving a fun memory together. Bonus happiness points if that memory makes you both laugh.

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Unsurprisingly sex also plays a role in relationship satisfaction, but that doesn't mean you have to do it 24/7. The happiest couples have sex twice or three times a week, but getting it on just once a week can make you 44 per cent more likely to have positive feelings.

Of course, even the most sickeningly happy couples fight sometimes — but it's how they go about it that makes a difference.

Unhappy couples are likely to hurl criticisms, show contempt, name call and act defensively (or just tune right out), while happier couples tend to diffuse the tension through humour, affection and by conceding on some arguments.

You can read more of Happify's findings here.

What makes you happy in a relationship?