The maths of infidelity (WS)

Summary

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Podcast Summary: More or Less – "The Maths of Infidelity" (WS)

Date: May 25, 2012
Host: Tim Harford, BBC Radio 4

Overview

This episode of More or Less takes a statistical deep dive into the commonly held belief that men are more unfaithful than women, questioning whether this holds up to scrutiny and what the data actually reveal. The show examines how infidelity is measured in social surveys, the reliability of self-reported data, and explores if it is mathematically possible for one gender to cheat more than the other. The episode also briefly covers a listener’s question about average salaries in Australia versus the UK, but the core focus remains on the “numbers behind unfaithfulness.”

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Key Discussion Points & Insights

1. Are Men Actually More Unfaithful Than Women?

• Setting the Stage

  • Tim Harford jokes about the predictability of the “adulterer’s journey,” referencing famous public denials and confessions (00:12–01:10).
  • Raises the canonical question: “Is it more likely that I’m cheating on my wife or that my wife is cheating on me?” (00:28)

• The Evidence

  • Fiona Woods (correspondent) highlights that there is “good evidence that men cheat more than women, and this isn’t just folk wisdom.” (01:32–01:41)
  • Reference to the 2006 American General Social Survey, where nearly twice as many married men as women admit to sex outside of marriage (01:45–01:57).

2. What Types of Men Cheat Most, and Why?

• Expert Testimony: Tom Smith, American General Social Survey (02:05–02:51)
  • Men in unhappy marriages or in legal separation are more likely to be unfaithful.
    • Quote: “Men who are in unhappy marriages are more likely to be unfaithful...people who travel a lot, people who are less religious tend to be more unfaithful.” (02:12–02:51)
  • These patterns are not unique to the US.

3. Infidelity Statistics in the UK

• UK National Survey of Sexual Attitudes and Lifestyles

  • Dr. Catherine Mercer explains how the large-scale British survey works and its methodology for sensitive questions (03:12–04:11).

  • Instead of asking directly about infidelity, they infer it by looking for overlaps in the timing of sexual relationships (04:17).

  • Quote: “Women are less likely to report that they cheat on their partners than men. But as it’s a socially sensitive behaviour, we can’t directly observe unfaithfulness. So we have to rely on what people tell us. And we know there are gender differences in how people report sexual behaviours.” (03:13)

  • Language Matters

    • Researchers prefer terms like “overlapping relationships” or “concurrent partnerships” over “infidelity” (04:40–04:47), especially important for epidemiological studies concerning STI/HIV transmission.

4. What Do the Numbers Actually Show?

• In 2000, the survey found that 15% of men reported overlapping or concurrent relationships in the past year, versus 9% of women (05:13).

  • Quote: “There is a gender difference and that is actually statistically significant.” (05:17)

• Mathematical and Reporting Caveats

  • There are caveats about how data is reported, for instance:
    • Women underreport sensitive behaviour more than men (03:12–03:52, 05:13–05:54).
    • Age differences in male/female partners can mathematically mean more men can be “unfaithful” even if their partners are single and thus not “cheating.”

5. Memorable Moments & Quotes

• Anecdotal Humor:
  • Tim quips about Fiona’s late nights: “So that’s your excuse for all those late nights at the office?” (01:29)
  • Fiona retorts: “It is. And be careful, because everyone knows men have a bad track record in this area.” (01:32)
• Data Nuance
  • Dr. Mercer: “Infidelity is quite a loaded word. Whereas thinking about overlapping partnerships is more appropriate when...thinking about the epidemiological context.” (04:47)
• Surveys’ Limitation Admission
  • Dr. Mercer emphasizes reliance on self-report and acknowledges, “we can’t directly observe unfaithfulness.” (03:20)

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Timestamps of Key Segments

• 00:12 – Tim Harford introduces the infidelity topic and common perceptions.
• 01:41 – American data: twice as many married men as women admit to infidelity.
• 02:12 – Tom Smith discusses risk factors for cheating.
• 03:13 – Dr. Catherine Mercer explains UK survey methods and challenges.
• 04:17 – How “infidelity” is measured via overlapping relationships.
• 05:13 – Actual gender difference statistics (15% men, 9% women).

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Additional Segment: Average Salaries in Australia vs. the UK (06:14–08:59)

Note: This is a brief statistical tangent, not related to infidelity.

• Listener from Australia wonders why he feels “below average” in pay terms, despite a comfortable salary.
• It’s revealed that currency exchange rates, the mining boom, and differences in wage calculations skew perceptions: Australians’ salary higher in nominal terms, but doesn’t buy as much as less in the UK on average (07:49–08:27).

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Conclusion

More or Less critically examines whether men are indeed more unfaithful than women and highlights how data is collected, interpreted, and the limitations of self-reported statistics. The takeaway: while survey data suggests men report more infidelity/concurrent partnerships than women, the exact numerical gap is shaped by social dynamics, reporting biases, and even definitional choices. The conversation balances statistical rigor with characteristic wit, making the numbers accessible—and thought-provoking.

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Notable Quotes

• Dr. Catherine Mercer (03:13):
  “Women are less likely to report that they cheat on their partners than men. But as it’s a socially sensitive behaviour, we can’t directly observe unfaithfulness. So we have to rely on what people tell us.”

• Tom Smith (02:12):
  “People who are away from home a lot…people who are less religious tend to be more unfaithful.”

• Dr. Mercer (04:47):
  “Infidelity is quite a loaded word. Whereas thinking about overlapping partnerships is more appropriate when we’re thinking about the epidemiological context…”

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Transcript

[A]

Thank you for downloading from the BBC. For details of our complete range of podcasts and our terms of use, go to bbcworldservice.com podcasts

[B]

this is more or less a slice of statistical lemon in the pleasant but confusing gin and tonic of media reporting. This week we'll ask whether men really are more unfaithful than women. Hello and welcome to More or Less the World in Numbers on the BBC World Service. Will make you wee this week. Is it more likely that I'm cheating on my wife or that my wife is cheating on me? Although presumably I should know something about at least one side of that equation. Infidelity. It happens perhaps more often than many of us would like to imagine. The adulterer's journey is a predictable one, moving from defiance I did not have sexual relations with that woman to acceptance.

[C]

Indeed, I did have a relationship with Ms. Lewinsky that was not appropriate.

[B]

But is it just as predictable that men are more inclined to commit adultery than women are? It is a very commonly held belief that men are less faithful than women. But it takes two to tango. So can this be mathematically possible? Fiona woods has been.

[D]

Well, actually.

[B]

What have you been doing, Fiona?

[E]

I've been looking at the numbers, Tim.

[B]

So that's your excuse for all those late nights at the office?

[E]

It is. And be careful, because everyone knows men have a bad track record in this area. There's good evidence that men cheat more than women, and this isn't just folk wisdom.

[B]

Indeed, there is actual data, and you've been looking at the American General Social Survey.

[E]

That's right. It's a 2006 study of 20,000 people, and it found that nearly twice as many married men as women admit to having had sexual relations with someone other than their spouse.

[B]

Men, eh?

[E]

Well, quite.

[B]

But we already suspected that. Our loyal listeners need to know more. What kinds of men are most likely to cheat?

[E]

Well, that's exactly what I asked Tom Smith of the American General Social Survey, and he warned me what to look out for.

[C]

Men who are in unhappy marriages are more likely to be unfaithful separated men. In other words, someone who is still technically married but is actually has a legal separation much more likely to take and have other partners during that stage of marriage. Even if that separation, of course, reconciles and does not lead to divorce, it still is a period in which infidelity tends to occur. People who travel a lot, people who are away from home a lot, people who are otherwise separated from their spouses for extended period because of work or travel or other reasons people who are less religious tend to be more unfaithful.

[E]

And the story is similar in other countries.

[B]

Yes. The National Survey of Sexual Attitudes and Lifestyles in the United Kingdom, for example, also finds that men are more likely to be unfaithful than women, although the researchers wouldn't put it exactly like that. I've been talking to the head of analysis for the national survey, Dr. Katherine Mercer, about exactly what such surveys are really measuring.

[D]

The bottom line is that women are less likely to report that they cheat on their partners than men. But as it's a socially sensitive behaviour, we can't directly observe unfaithfulness. So we have to rely on what people tell us. And we know that there are gender differences in how people report sexual behaviours. So the National Survey of Sexual Attitudes and Lifestyles is a large probability survey of people aged 16 to 74 living in Britain, and people are randomly selected to be invited to participate. People are asked less sensitive questions, initially, for example, about how they learned about sex, their general health, contraception use, and then for the more sensitive questions, for example, about the numbers of partners they've had, the type of sexual practices they engage in, we use self interview. So the respondent reads the question from a laptop screen and answers their response directly into the computer.

[B]

What are the actual questions that you're asking in order to deduce that people have been unfaithful? Well, maybe you just ask them straight out.

[D]

Well, there have been two previous Nat out studies and we didn't actually ask people outright, have you been unfaithful? Instead, we've used the dates of first and most recent sex with their most recent partners. And we looked then to see if the dates overlap, to see if there's any evidence that perhaps those partnerships were overlapping.

[B]

Is this the language that you guys in Natzel use? I mean, do you talk about overlapping sexual relationships rather than talking about infidelity?

[D]

Anyway, we do. Infidelity is quite a loaded word. Whereas thinking about overlapping partnerships is more appropriate when we're thinking about the epidemiological context of these data, we're thinking, for example, about the importance of overlapping partnerships or concurrency for the transmission of sexually transmitted infections and hiv.

[B]

Ok, so what are the headline rates of concurrent sexual relationships as measured by the survey?

[D]

Using that method, we found last time in 2000 that 15% of men had had overlapping or concurrent partnerships in the last year, in contrast to 9% of women. So there is a gender difference and that is actually statistically significant. There is evidence as well to suggest that there could well be a gender difference in unfaithfulness when we think about the age difference between sexual partners. So, for example, we know that on average men tend to be slightly older than their female partners. And so if you imagine a scenario where a married man has an affair with a younger woman who's perhaps more likely to be single because she's younger, then he would have engaged in unfaithfulness, but she wouldn't have done.

[B]

Dr. Catherine Mercer of the Centre for Sexual Health and HIV Research at University College London and of course, our very own Fiona Woods. Thank you, Fiona. And now I'm joined by Ruth Alexander. And Ruth, we've had a cry for help this week from Australia.

[F]

We did.

[G]

My name is Gerard Butlin. I'm a regional manager with the pharmacy chain out here in South Australia, in Adelaide. I was wondering about the fact that the average salary that they seem to be portraying in Australia is massively higher than the average salary that seems to be paid in the uk. So I'm out here with a fairly responsible job, company car, company phone, all the bits and pieces. I feel very comfortable, but I'm still eight grand shy of the average. So I was just wondering, are they counting different things in Australia or is it that the mining millions are pulling up the average? If you could shed any light on it, it would be very much appreciated because I'd like to feel a little more average.

[F]

So Gerard wants to know why, when he thinks he's doing pretty well, he remains statistically below average. And he wonders why Australians seem to be paid so much more than Brits 1,350 Australian dollars a week, or £850, almost £250 more than the average UK weekly salary.

[B]

And it's also above the average salary for the OEC of rich countries too.

[F]

Now, your country's average salary is a number you may feel, you know, it's the sort of number that is widely quoted, but to really know it, you have to understand its complexities.

[B]

And those are the bits we often don't hear about.

[F]

Yes. For instance, the average salary might be quite different from the kind of salary earned by the average person. If a few people are making loads of money, that will raise the average.

[B]

And Gerard's wondering about this kind of thing, whether the average salary is skewed by people earning a ton in the

[F]

mining industry and mining wages are higher than most. But. But those people are a small proportion of the labour force as a whole, so mining can't have pulled up the average by very much.

[B]

So there must be Something else going

[F]

on and actually it is something to do with mining. Australia's enjoying a mining boom at the moment and this has driven up the exchange rate.

[B]

Meanwhile, the pound sterling is weak and so much of the apparent difference is down to the exchange rate between the two countries. The mining boom means Australia is feeling rich. Wages are high, but so are prices.

[F]

So, in fact, although the average pay packet is higher in Australia, it doesn't quite stretch as far as the average UK pay packet does, or the average OECD pay packet, in fact. And that is, you can buy slightly more if you're on the average wage in the UK than if you're on average pay in Australia.

[B]

And so all that means in simple terms. Well, I hate to say it, really.

[F]

Yes, it is a bit awkward. I phoned Gerald to let him know I tried to be gentle. We've looked at it from all different angles and our conclusion is that actually, you are below average.

[G]

Fantastic. In a way. In one way it's encouraging, you know, it's a bit aspirational. Well, you know, I've got to keep on plugging to get to be an average, but on the other, it's a bit annoying.

[B]

Poor old Gerard. Well, thank you, Ruth. That's all we have time for this week. Please keep your comments and suggestions coming in to More or [e-mail] we love using your suggestions and your questions in the program. And don't Forget our website, bbcworldservice.com more or less, where you can subscribe to our podcast. We'll be back next week with more number Y. Goodness. Until then, goodbye. More or Less was presented by me, Tim Harford, the undercover economist at the Financial Times. The producer was Richard Knight and the editor, Richard Varden.

[A]

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