Researchers in the United States and Norway are working together to figure out what forms of flirtation are most effective and why.

The results of the international collaboration are only based on questionnaires, not experiments, which means we have to assume participants are being honest and self-aware about what they find attractive.

That said, among 415 men and women in Norway and 577 in the US, there was one way of flirting that stood out among heterosexual relationships.

Whether looking for a fling or a long-term romance, humor was generally deemed the most effective strategy.

For both genders, laughing at someone else's jokes was considered advantageous. But cracking jokes was perceived to be the most useful strategy for men, especially those looking for long-term relationships.

"It is not only effective to be funny, but for women it is very important that you show your potential partner that you think they are funny," says evolutionary psychologist Rebecca Burch from the State University of New York at Oswego.

Let's be honest, the results feel a little bit 'icky' – we're not endorsing anyone try these kind of strategies at home. But from a scientific perspective there's some interesting stuff to dig into. The results support a sexual strategies theory for flirtation, which arose in the 1990s.

Over the years, studies on this underlying theory suggest that women looking for short-term relationships are the most effective at flirting when they make their sexual availability known.

Men, on the other hand, are better off displaying commitment and generosity while flirting with the opposite sex.

The theory argues this is due to pressures of sexual selection in the human species. For men, sex comes with minimal obligations or investment in an offspring, so, according to evolutionary theory, they are more likely to have multiple partners. Women, on the other hand, need to be pickier about their prospects.

Practically, this would mean the most effective female flirts were those who made sexual advances obvious and known, through behaviors like physical contact.

The most effective male flirts, meanwhile, would be those who reigned in their sexual desires and who instead promoted the best parts of their person.

Using a set of common flirtation tactics, put together in 2016, researchers in the US and Norway have now tried to reproduce that underlying theory.

The questionnaire given to participants measured responses to 40 flirtation tactics, including cues of sexual availability, like "moves closer" and "touches foot", or cues of investment and commitment, like "gives you flowers".

Other flirting tactics on the list included non-intimate communication, like "asks for your help", and humor production, like "makes you laugh".

In both cultures, the results were surprisingly similar, despite the US and Norway being ranked very differently when it comes to sexual liberalism.

Both men and women in the study reached a consensus on which flirtation tactics were the most effective, and in which scenarios they were most effectively used.

For women looking for a fling, the study found signals of sexual availability, like "dressing sexy" or "physical contact" were judged the most effective. Meanwhile, less sexual, friendly contact was not.

For men, flirtation tactics that signal generosity and commitment, like "intimate conversation" and "spending time together", were thought to be the most effective. This was especially true when men were looking for a long-term relationship.

Interestingly, when men were looking for a short-term relationship, the authors found that contact through comments, chats and compliments were not as effective forms of flirtation.

In a long-term relationship, however, these tactics were just as effective as "intimate conversations".

"Verbal investment or committed attention, such as light conversations/chats, compliments, random comments, and texts, even if it is not prolonged or intimate, may signal continued (even if small) investment," the authors admit.

As expected, humor ranked very high as an effective flirtation tactic.

Participants in the study agreed that laughing at a joke is effective for both men and women. But when it comes to actually cracking the jokes, this type of flirting is thought to be more useful for men, especially ones looking for long-term relationships.

The authors suspect that is because humor is a hard-to-fake sign of intelligence, creativity and agreeableness. As a result it's a good indicator of a future partner with a positive influence on a woman's well-being.

The results of the questionnaires are interesting, but they are by no means indisputable. The surveys provide an intriguing view into heterosexual relationships, but the ranking system is simplistic and doesn't take into account the complex realities of flirting, which are based on far more than what a person says or does.

The findings from the surveys do, however, suggest that our ideas around effective flirting are quite gendered and situation-specific, and that these notions exist across western cultures.

The study was published in Evolutionary Psychology.