WS MoreOrLess: Is strenuous jogging bad for you?

Summary

More or Less: Is Strenuous Jogging Bad for You?

BBC World Service, Feb 9, 2015
Host: Tim Harford

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Episode Overview

This episode addresses the concern sparked by a BBC article suggesting that "too much jogging is as bad as no exercise at all." Host Tim Harford and guest Dr. Alicia White scrutinize the research behind these headlines, questioning whether strenuous jogging truly poses mortal danger. The episode also debunks another sensational statistic—this time about alleged infidelity aboard cruise ships.

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Key Discussion Points and Insights

1. Interrogating the Jogging Study ([00:19]–[05:31])

• Study Background

  • A BBC article stirred worry by claiming strenuous jogging could be as harmful as no exercise.
  • Many listeners expressed concern, including Manya: "I feel very healthy and wonder how close to death am I really?" ([01:05] Dr. Alicia White quoting listener)
  • The study referenced was published in the Journal of the American College of Cardiology.

• What Did the Study Actually Do? ([01:41])

  • Dr. Alicia White explains the study grouped participants based on:
    • Whether and how much they jogged per week
    • Frequency of jogging per week
    • Self-reported pace: slow, average, fast
    • Comparisons to a sedentary group (no exercise)
  • Over 10–12 years, researchers tracked mortality rates across these categories.

• Defining 'Strenuous Jogging' ([02:11])

  • "Strenuous joggers" were those who jogged fast, for 2.5–4+ hours a week, more than 3 times per week.

• Notable Quote:
  Tim Harford: "I just wanted to ask how many people in the strenuous jogger category actually died?" ([02:45])
  Dr. Alicia White: "Two." ([02:57])
  Tim Harford: "That doesn't sound like a lot."
  Dr. Alicia White: "No, it's not."

• The Problem of Small Numbers and Overinterpretation ([03:06])

  • With only two deaths in the strenuous jogging group (out of ~36 people), statistical certainty is very low.
  • Dr. White: "With such small numbers, we really can't say with any level of certainty whether the proportion who died in that group is different to those in the sedentary group." ([03:10])

• What Did They Die Of? ([03:56])

  • No information on causes of death—could have been unrelated to jogging.

• Sample Size Limitations ([03:36])

  • Although the study was "relatively large," the strenuous jogging subgroup was small (~36 people).

• What Conclusions Are Reasonable? ([04:15])

  • Light joggers had lower mortality than sedentary people.
  • For strenuous joggers: "I wouldn't be able to say with any confidence whether you were less or more likely to die or just the same as sedentary non joggers. Based on this study alone." ([04:30] Dr. Alicia White)

• Why Do Headlines Exaggerate? ([04:57])

  • Dr. White suggests: "People get bored with a standard message... Moderate exercise is good for you. Or light to moderate exercise is good for you." ([05:00])
  • The "dangerous levels of jogging" angle is simply a more intriguing spin.

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2. Debunking Cruise Ship Cheating Claims ([05:31]–[09:19])

• Media Claim Under Review

  • The UK Daily Telegraph reported: "One in five passengers admit to cheating on their partner on a cruise ship, 80% while their partner was on board."

• How the Survey Was Conducted ([05:31])

  • Performed by Cruise.co.uk, posted as a forum question.
  • Fewer than 300 responded.

• Breaking Down the Numbers ([06:15])

  • Q1: "Have you ever had sex on a cruise?" → 81% said yes.
  • Q2: "Was it with someone other than your partner?" → 17% said yes (basis for 'one in five cheat' claim).
    • Harford points out, "if you were single and had a fling, you'd have answered yes. And ... a holiday romance isn't cheating ... if you were single when you started." ([06:35])

• Misinterpretation of Results

  • Subsequent questions further muddy conclusions about infidelity.
  • Many 'yes' responses don't necessarily indicate cheating.

• Quote:
  "All the survey shows is that most people have had sex on a cruise with their partner." ([08:10] Tim Harford)

• Advice to Worried Listeners

  • Listener Justin asked: "Should I cancel my cruise and save my marriage?"
  • Harford reassures: "Please don't cancel your cruise. It sounds like you might have a lot of fun." ([08:45])

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Notable Quotes and Memorable Moments

• Tim Harford, on BBC headlines:
  "Too much of anything is excessive. But that's not really a fact about jogging. That's a fact about how the English language works." ([00:35])

• Dr. Alicia White, on interpreting low death counts:
  "With such small numbers, we really can't say with any level of certainty..." ([03:10])

• On sensational media reporting:
  "People get bored with a standard message... moderate exercise is good for you." ([05:00] Dr. Alicia White)

• Closing tongue-in-cheek comfort to cruise-goers:
  "Please don't cancel your cruise. It sounds like you might have a lot of fun." ([08:45])

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Timestamps for Important Segments

• [00:19] - Tim Harford introduces the jogging debate
• [01:41] - Dr. Alicia White begins analysis of the jogging study
• [02:45] - Strenuous jogging category: Only two deaths
• [04:15] - Dr. White summarizes what can and cannot be said based on the study
• [05:31] - Switch to analysis of the cruise ship cheating statistic
• [08:10] - Harford dismantles media claims about infidelity on cruises
• [08:45] - Final reassurance to worried listener Justin

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Summary

Jogging:
The episode dismantles media hype around jogging risks, emphasizing that light or moderate jogging is associated with lower mortality than no exercise. Claims about the dangers of strenuous jogging rest on extremely small, statistically unreliable samples.

Cruise Infidelity:
Similarly, the much-publicized survey about cheating on cruises is exposed as a statistical mess. Poorly worded survey questions and misinterpretation by journalists lead to misleading headlines.

Overall:
The episode humorously and incisively shows how numbers can be misrepresented, urging listeners to look beyond sensational headlines and focus on what the data genuinely support.

Transcript

[Dr. Alicia White]

This is the short edition of More

[Tim Harford]

or Less, first broadcast on the BBC World Service.

[BBC Announcer]

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

[Tim Harford]

hello and welcome to More or Less on the BBC World Service. We're the balsamic vinegar on your statistical salad and I'm Tim Harford. Let's talk about jogging. Is it a convenient way to keep fit or a steady plod towards the chill solitude of the grave? Because, as the BBC rather unhelpfully reported this week, too much jogging, as bad as no exercise at all, which doesn't tell us a lot. The clue's in the phrase too much. Too much of anything is excessive. But that's not really a fact about jogging. That's a fact about how the English language works. Anyway, soon messages came flooding in to more or lessbc.co.uk. some were sceptical and some rather worried.

[Dr. Alicia White]

I feel very healthy and wonder how close to death am I really?

[Tim Harford]

Asked Manya, who regularly jogs more than two and a half hours a week at a pretty good pace. The BBC article was referring to a study published in the Journal of the American College of Cardiology. So we decided to turn to somebody who'd analyzed it. Hello, Dr. Alicia White of Bayesian, which is a consulting firm specialising in clinical evidence. I asked her what the researchers had done.

[Dr. Alicia White]

They assessed whether people jogged and if they did jog, how much they jogged, how fast they jogged, how frequently they jogged. And then they also looked at a group of people who were essentially sedentary, who didn't do very much exercise at all. And then it followed those people up over about 10 to 12 years to see who died within that period.

[Tim Harford]

They were pulled into various groups. So the sedentary group and the light jogging, the moderate jogging, what was the definition of strenuous jogging?

[Dr. Alicia White]

So, first of all, they split them according to essentially the quantity of jogging. So how many hours a week did they do? They also looked at the frequency of jogging. So how many times a week did they jog? And also jogging pace. So this is self defined jogging pace. Did they think they were slow, average or fast? And the strenuous joggers, they were the ones who tended to be jogging at a fast pace, between two and a half and four hours, over four hours a week, and often very frequently. So usually above three times a week.

[Tim Harford]

And then we were told this notorious result, that too much jogging is bad for you. I just wanted to Ask how many people in the strenuous jogger category actually died?

[Dr. Alicia White]

Two.

[Tim Harford]

Two?

[Dr. Alicia White]

Yes, two.

[Tim Harford]

That doesn't sound like a lot.

[Dr. Alicia White]

No, it's not.

[Tim Harford]

And it could easily have been 1 or 3 or 0.

[Dr. Alicia White]

Yes, it could have been. That's the issue really is that we can't say with such small numbers, we really can't say with any level of certainty whether that the proportion who died in that group is different to those in the sedentary group.

[Tim Harford]

So is this just a case of a study that didn't look at enough people, or is it that just the number of people in that particular category of strenuous joggers wasn't big enough to form firm conclusions?

[Dr. Alicia White]

I think it was a relatively large study, but yes, I would say that in the strenuous group, the number of people in there. So it was about 36 people when they looked at the people who had all of the data available, that it's not large enough for that group alone to be able to tell you with confidence about the effects on death in that group.

[Tim Harford]

And these two people, they could have died from anything. They could have choked on a pint of beer or fallen off a cliff or it could be anything at all.

[Dr. Alicia White]

Yes. There's no information provided in the study about what these two people died from. And they themselves say that they can't analyze the effects on different causes of death. So this is just deaths from any cause at all.

[Tim Harford]

So would a more reasonable reading of this study be to say that people who engage in light exercise live longer than people who don't exercise and we can't really say very much about people who engage in stress exercise because we didn't have enough of them in our study.

[Dr. Alicia White]

Yes, I think that's reasonable. Essentially those who engaged in light jogging, and this is very specifically jogging, it didn't look at other forms of physical activity, did tend to be less likely to die of a follow up than those who didn't engage in exercise? So those who are sedentary, but yes, with strenuous jogging, I wouldn't be able to say with any confidence whether you were less or more likely to die or just the same as sedentary non joggers? Based on this study alone, why do

[Tim Harford]

you think people got so excited about the study in the media?

[Dr. Alicia White]

Well, it's difficult to say, but I think sometimes people get bored with a standard message, which is essentially what this is saying, which is, you know, doing some exercise is good for you instead of sort of focusing on that aspect of the study. I think maybe sometimes the oh, actually maybe lots of exercises is no good for you at all, is a different spin to put on it to make it a more interesting study than what a surprise. Moderate exercise is good for you. Or light to moderate exercise is good for you.

[Tim Harford]

Alicia White. Now what could be more romantic than a relaxing cruise on the Mediterranean Sea? You take your loved one by the hands and recreate that magical Jack and Rose moment from Titanic. The salty sea breeze is whipping through your hair. The evening is enchanting. You learn to carve love hearts out of watermelons. Then the Michael Bubble tribute, then the Michael Buble tribute act sings your song. It is perfect. Just you and that special person to whom you've pledged your heart. Or maybe that fit young pool attendant. Because according to research published in the UK newspaper the Daily Telegraph, the typical cruise these days is less the Love Boat and more the the Love Rat, her steamy orgy of depravity and betrayal. Where was I? The Telegraph's article makes it clear that nothing could be more catastrophic for the devoted monogamist than a cruise. One in five passengers admit to cheating on their partner on a cruise ship. To add insult to injury, in 80% of those cases the partner was on board. Concerned listener Justin has emailed us to ask, should I cancel my cruise and save my marriage? Justin, don't take any drastic action. Just lie back on your sun lounger and close your eyes while we look into these numbers. This survey was carried out by Cruise Co.uk and website for Cruise enthusiasts. It posted some questions about onboard sex in its forum and fewer than 300 people answered. First, the survey asked, have you ever had sex on a cruise? 81% of people responded yes. Perhaps not surprising, it continued, was it with someone other than your husband or wife or partner? 17% of respondents said yes. And that's where the Telegraph gets its claim that one in five passengers cheats. But that's not what the question asked. For example, if you were single and had a fling on board, you'd have answered, yes. And I'm sorry to drag the Daily telegraph into the 21st century, but a holiday romance isn't cheating on anybody if you were single when you started. For that matter, if the cruise was years ago and you were sleeping with the person who was your partner at the time but isn't your partner now, then you might also have responded, yes, and that's not cheating either. And now the real statistical bungle. The survey's next question was your husband or wife or partner on board at the time, 81% of people responded yes to that. And the Telegraph concludes from this that 80% of people have cheated while their partner was on board. But again, that's not what this number shows. Remember, 81% of people said they'd had sex, 83% said it was with their current partner or spouse and then 81% said their partner or spouse was on board. So all the survey shows is that most people have had sex on a cruise with their partner. So Justin, our dear listener, please don't cancel your cruise. It sounds like you might have a lot of fun. Thank you for listening. We love hearing from you too. You can email your comments and questions to us and our address is more or less bc.co.uk. and you can download this program and many previous editions at our website BBC.commoreorless

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