It's the age-old question many of us have daydreamed about or discussed over a few drinks at the pub.
But now researchers say it's official - having lots of s*x does make for a better relationship - but most of us either don't realise or won't admit it.
Married couples who have s*x frequently have increased 'unconscious' relationship satisfaction, a study found.
While couples who have s*x often do not seem more satisfied with their relationship, they are more likely to experience positive spontaneous gut feelings towards their other halves.
The finding, published in the journal Psychological Science, may help explain previous studies suggesting sex does not improve happiness levels.
Doctoral student Lindsey Hicks, of Florida State University, said: 'We found the frequency with which couples have s*x has no influence on whether or not they report being happy with their relationship.
'But their sexual frequency does influence their more spontaneous, automatic, gut level feelings about their partners.'
She added: 'This is important in light of research from my colleagues demonstrating these automatic attitudes ultimately predict whether couples end up becoming dissatisfied with their relationship.'
Scientists say that in evolution, frequent s*x has several benefits including improving chances of conception and bonding partners in relationships to help child rearing.
But when researchers explicitly ask couples about their relationship satisfaction, they typically do not find any association between satisfaction and frequency of s*x.
'We thought these inconsistencies may stem from the influence of deliberate reasoning and biased beliefs regarding the sometimes taboo topic of sex,' Ms Hicks explains.
Our gut level, automatic attitudes do not require conscious deliberation so the researchers think they may tap into implicit perceptions or associations to which we are oblivious.
They decided to tackle the question again, assessing partners' relationship satisfaction using both standard self reports and instinctive measures, known in psychology as automatic behaviour.
In the first part of the study, 216 newlyweds completed survey style questionnaires about their relationship satisfaction, rating various qualities of their marriage, for example bad-good, dissatisfied-satisfied and unpleasant-pleasant.
They were also asked about the extent to which they agreed with different statements such as 'we have a good marriage', and their overall feelings of satisfaction with their partner, their relationship with their partner and their marriage.
Then, they completed a computer task where a word appeared appeared on screen and they had to press a specific key to indicate whether it was positive or negative.
Prior to this a photo of their partners flashed up for a third of a second. The rationale behind this kind of implicit measure is that participants' response times indicate how strongly two items are associated at an automatic, or instinctive, level.
The faster the response time, the stronger the association between the partner and the word that appeared.
Responding more slowly to negative words than to positive words that followed the picture of the partner would signify generally positive implicit attitudes toward the partner.
The researchers also asked each partner in the couple to estimate how many times they had had s*x in the last four months.
Just as in previous studies, Ms Hicks and colleagues found no association between frequency of s*x and self reported relationship satisfaction.
But when they looked at participants' automatic behavioural responses, they saw a different pattern.
Estimates of sexual frequency were correlated with participants' automatic attitudes about their partners.
That is, the more often couples had s*x, the more strongly they associated their partners with good attributes.
Importantly, this finding held for both men and women. And a longitudinal study that tracked 112 newlyweds indicated frequency of sex was in fact linked with changes in participants' automatic relationship attitudes over time.
Ms Hicks said: 'Our findings suggest we are capturing different types of evaluations when we measure explicit and automatic evaluations of a partner or relationship.
'Deep down, some people feel unhappy with their partner but they do not readily admit it to us, or perhaps even themselves.'
The researchers note participants' reports of how often they remember having sex may not be the most precise measure of sexual frequency.
And it remains to be seen whether the findings are applicable to all couples or specific to newly married couples like those they studied.
Last year a study by Canadian researchers found happiness peaks when couples have sex once a week, but does not increase with greater frequency.
And another by a team in the US said encouraging couples to have more sex actually made them more miserable.
But Ms Hicks said taken together, her findings drive home the point asking someone about their feelings or attitudes is not the only way to measure how they feel.
Ms Hicks added: 'These studies illustrate some of our experiences, which can be either positive or negative, affect our relationship evaluations whether we know it or not.'