If you haven't had any action recently, you are not alone. Look at the data for your age and gender here

When you look at a spreadsheet of numbers, it's useful to think about the people behind them. So, when I saw the percentage of 25 to 34 year olds that haven't had sex in the past four weeks, I asked my friends at dinner what they thought the number would be.

And a funny (albeit slightly predictable) thing happened: those that hadn't had sex recently guessed a much higher percentage than those that had. Paul (in a long-term relationship) guesses 7% of men his age haven't had sex in the past four weeks while perpetually single Chris puts it at 55%.

Both of them are wrong, a lot wrong. The National Survey of Sexual Attitudes and Lifestyles asks 15,000 British adults about their sexual experiences through face-to-face interviews. But some more sensitive questions are reserved for a self-completed questionnaire.

One of those sensitive questions is "have you had any sex in the past four weeks?". The chart below shows the percentage of respondents that said no (if you're on mobile click here).

What's happening?

Depending on who you are and what assumptions you have about sexual activity, these results from the Medical Research Council might surprise you. For me, one anomaly jumps out straight away: the gap between men and women.

On average, there is an 8 percentage point difference between the men and women who answered. That's a considerable gap that would mean millions more men than women have had sex in the past four weeks. There seem to be four possible explanations for that discrepancy.

1. Homosexual men outnumber homosexual women and they have more sex

2. Several men are sleeping with the same woman - and that situation is being repeated nationwide

3. Men are more more likely to lie to make it seem that they're having more sex

4. Women are more likely to lie to make it seem like they are having less sex

Without more data on sexual preferences and attitudes, it's not possible to work out which of those is the case.

The missing virgins

Explanations 3 and 4 above show how important wording is. Asking 'have you had any sex in the past four weeks?' could elicit very different responses to 'has anyone willingly had sex with you in the past four weeks?'.

In fact, even the four weeks bit is very important. Those bars in the chart above represent people that haven't had sex in the past four weeks, but they also represent people that haven't had sex in the past four months, the past four years and even people that have never had sex. But because there's only one question, phrased in only one way, it's not clear how that breaks down.

There is one company that thinks they do know, because their profitability depends on them knowing: Durex. Only, rather than calling it 'virginity' they keep a close eye on 'age at first sex' and they seem to know a lot about it. For example, their 2007 survey found that PhD students will on average have their first sexual experience at 20.25 years, compared to 19 years for those who never completed university. Silver linings maybe.

Durex even claim to know how the age at which people first have sex varies between countries. Malaysia has the highest average age in the world (23.7 years) and it also has the highest rate of confidence (42% of Malaysians felt they were ready for that first sexual encounter). Silver linings maybe.

By contrast, Austrians feel almost as confident (38% of the said they were ready) even though the average age they first have sex is considerably younger; 17.5 years old. So clearly, age isn't everything.

The Durex survey may have had over 26,000 responses but we're not necessarily any more persuaded by it than the academic one mentioned above. You can explore their findings on virginity around the world in the map and, if you want to contribute your own data, fill in our anonymous survey below (or here on mobile).

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Take a look at the data here (the results above are only for healthy adults, those that are in poor health have lower rates of sexual activity) and share your views on its reliability below.

For all of you keen to be a part of our data journalism, we'll write about the data you contribute in the form above next Friday.