What price the life of a badger?

Summary

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More or Less – "What price the life of a badger?" (BBC Radio 4, August 30, 2013)

Host: Tim Harford
Main Topics: The value of a badger’s life in the context of the cull, NHS hospital death statistics, climate migration figures, and the realities of big data and privacy.

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Episode Overview

This episode, which launches a new series of More or Less, delves into several high-profile statistical claims and explores the underlying numbers driving contemporary debates. The show critically examines the economics behind the badger cull in England, scrutinizes widely-reported NHS mortality statistics, questions dramatic claims about climate change migration, and demystifies the "big data" phenomenon and its implications for privacy.

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Key Segments & Insights

1. The Value of a Badger’s Life: Economics of the Cull

(00:13 – 05:57)

• Context: England proposes culling badgers to fight the spread of bovine TB, sparking heated debate.
• Core Issue: How do you incorporate the value of a badger’s life into cost-benefit analyses of culling?
• Govt’s Cost-Benefit Analysis: Considers the cost of cattle and bullets, but not the "value" of a badger’s life.
• Chris Cook (Financial Times):
  • "It's actually something of a philosophical question, but they do undoubtedly have a value and we can tell that because people really care when you shoot badgers." (02:33)
  • Observes that setting the value to zero is unrealistic given public sentiment.
• Practical Challenge: How many badgers are there?
  • Rosie Woodruff (Zoological Society of London) explains counting badgers is complex due to their nocturnal habits and social structures.
    • "You have to know how many badgers there are. But as it turns out, counting badgers is really difficult." (04:13)
  • Govt estimates: ~3,400 badgers in West Gloucestershire, ~2,500 in West Somerset (uncertainty exists, e.g., 1,972–2,973 in West Somerset).
• Policy Puzzle:
  • Licenses may require killing more badgers than actually exist due to estimation errors.
  • "Farmers are being legally required by their licenses to cull more badgers than actually may be present in the area." —Rosie Woodruff (05:50)

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2. NHS Mortality Statistics: Interpreting Hospital Death Figures

(06:35 – 12:44)

• Media Claim: 13,000 people "needlessly died" at England’s worst-performing NHS trusts.
• The Metric: Hospital Standardised Mortality Ratio (HSMR) – compares actual deaths to expected deaths.
• Tim Harford: Points out the 13,000 figure doesn’t appear in Sir Bruce Keogh’s review.
• Sir Bruce Keogh (NHS Medical Director):
  • "...it is clinically meaningless and academically reckless to use such statistical measures to quantify actual numbers of avoidable deaths." (07:12)
• Professor Brian Jarman: Emphasizes HSMR isn’t a direct measure of avoidable deaths.
• Statistical Insight: Around half of trusts will always be below average—“should shock nobody.”
• Professor Nick Black (LSHTM):
  • Fiercely critical of HSMR as a simplistic number for complex problems:
    • "For every complex problem, there is a simple solution and it's wrong." (10:52)
  • HSMR can flag issues but shouldn’t be used for actual avoidable death counts.
  • Better approach: Detailed reviews of deaths in each trust suggest ~5% of hospital deaths are avoidable — about 12,000 per year.
  • Moving forward, all hospitals will review ~100–120 deaths annually for detailed analysis.

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3. Climate Migration Stats: The Reality Behind the Numbers

(12:44 – 21:23)

• Claim Reviewed: "20 million people displaced by climate change in 2008... UN estimates 200 million climate refugees in future." —Chris Bryant, Labour’s immigration spokesman.
• Expert Voices:
  • Alex Randall (Climate Outreach):
    • Critiques lumping all natural disaster displacement under "climate refugees":
      • "The relationship between natural disasters and climate change is complicated... it's certainly not the case that we can attribute all of those individual displacements to climate change alone." (14:43)
    • Most displacement is local and temporary.
• Examining the 200 Million Figure:
  • Originates from scientist Norman Myers, not the UN, based on crude and questionable assumptions.
  • The UN used the figure but later distanced itself from it.
  • Stephen Castles (Oxford):
    • "He simply took a map of the world, worked out what areas would be inundated... and then simply assumed that all the people affected... would have to migrate." (18:36)
• Insight:
  • Real cases are usually local (e.g., small Pacific islands like Tuvalu, with populations in the thousands—not millions).
  • General conclusion: Dramatic migration figures are likely exaggerated; both the method and actual scale are questionable.

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4. Big Data: Promise and Privacy

(21:37 – episode end)

• The Hype: "Big Data" is used to market management books and consulting, but what does it really mean?
• Expert Definitions:
  • Mark Elliot (Manchester University):
    • "The main features of big data in its current form that are interesting... are the fact that it's real time data and that it's linked data." (22:15)
    • Real-life implications: Linking government policy, supermarket data, and health to understand effects dynamically.
• Privacy Challenge:
  • Data that is "anonymized" can often be re-identified.
  • Ed Felton (Princeton):
    • Describes "mosaic effect":
      • "...assembling small pieces of data from different sources... from which an identity emerges." (24:53)
    • Netflix example: Researchers publicly re-identified individual users by combining Netflix data with IMDb.
    • "What appears to be very innocent data could actually be revealing very, very personal facts about people." —Tim Harford (26:43)
  • On trade-off: "Companies are not very transparent about their practices. I think we could do better... by more transparency and a more honest conversation." —Ed Felton (27:08)

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Notable Quotes & Memorable Moments

• On valuing badgers:
  • "The correct valuation of a badger's life is [surely not] zero." —Chris Cook (03:35)
• On NHS deaths statistic:
  • "It is clinically meaningless and academically reckless to use such statistical measures to quantify actual numbers of avoidable deaths." —Sir Bruce Keogh (07:02)
• Big Data privacy insight:
  • "In all cases, it involves assembling small pieces of data from different sources and putting them together to make a kind of mosaic from which an identity emerges." —Ed Felton (24:53)
• On climate migration estimates:
  • "[Myers] simply took a map... worked out what areas would be inundated if the sea rose... and then simply assumed that all the people... would have to migrate." —Stephen Castles (18:36)

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Segment Timestamps

• 00:13 – Opening theme; introduction to key topics.
• 01:38 – Govt’s badger cull: cost-benefit question.
• 02:01 – 03:41 – Chris Cook on how badger lives are valued in economics.
• 04:13 – 05:57 – Rosie Woodruff on the problems with counting badgers.
• 06:35 – 12:44 – Detailed breakdown of NHS hospital mortality statistics.
• 13:11 – 21:23 – Debunking the numbers behind climate migration.
• 21:37 – 27:27 – Explaining Big Data; discussion of privacy and re-identification.
• 27:27 – Final contact details and closing remarks.

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Summary & Takeaways

The episode embodies More or Less’s critical and occasionally tongue-in-cheek approach to numbers in public debate:

• Animal economics is fraught with ethical and measurement pitfalls.
• Healthcare statistics are easily misunderstood; beware of grossly simplified headlines.
• Climate migration numbers circulate with little basis, often inflated by advocacy rather than science.
• Big Data offers insight and risk: anonymization is not foolproof, and transparency is lacking.

Listeners are reminded to be skeptical of big numbers and simple stories—and that numbers, like badgers, deserve careful consideration.

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Transcript

[Tim Harford]

Thank you for downloading More or Less from the BBC. This is the version of the programme first broadcast on BBC Radio 4. Here's Tim Harford.

Hello and welcome to a brand new series of More Or Less the programme which strikes fear into the heart of statistical vagabonds across the galaxy. This week, our clumsy or uncaring staff in English hospitals really killing thousands of patients. We'll ask how many people are being driven to flee their home country by climate change? And always down with the cool kids. We'll talk about this buzz phrase big data. But first, badgers. The lovable little rogues have, alas, been firmly implicated in playing some sort of role in infecting cows with tuberculosis, which is expensive for farmers and not much fun for the cows either, who are put down if they get tb. One possible approach is to kill a bunch of badgers in the hope of reducing bovine tb. Harsh on the badgers, but then they are much less delicious than cows. Cue strong feelings on both sides of the debate. The anti cull protesters are even able to count the Queen guitarist, Brian May among their number.

[Brian Jarman]

I really love you.

[Tim Harford]

You're my best friend. Now, Owen Patterson, who's the Secretary of State in charge of killing badgers and who also runs defra, the Department for Environment, Food and Rural affairs, has backed a cull of badgers being carried out by farmers in Somerset and Gloucestershire. But he reckoned without Evan Davies of the Today programme, who floored him with this question.

[Nick Black]

Just out of interest in the cost

[Tim Harford]

benefit, which I know you have done

[Nick Black]

at defra, what price is put on the life of a badger?

[Tim Harford]

I'm not putting a price on a badger. I'm probably the only person listening to

[Chris Cook]

this programme that had pet badgers as a child.

[Tim Harford]

Well, the minister seemed not quite to grasp what Evan was driving at. Many people don't quite grasp what Evan was driving at, but one man who does is Chris Cook of the Financial Times.

[Chris Cook]

So Evan's question was undoubtedly a bit bizarre, but actually spoke to an incredibly fundamental question in public policy, which is, when you do a cost benefit analysis, you have to make sure that you include as many of the relevant costs as and benefits when you do that. Now, some of those costs and benefit can be relatively easily ascertained. So we know what the cost of a head of cattle is. For example, we just go down to an auction, listen in and find out what people are willing to pay for a cow. It's much harder to work out what's the value of the life of a badger. It's actually something of a philosophical question, but they do undoubtedly have a value and we can tell that because people really care when you shoot badgers. And now it is very peculiar that in the government's cost benefit analysis, it's sort of. It's the cost of the bullets that's really the limitation on how many badgers you kill. It's nothing about the badger, it's not enthusiasm for the badger. There is no care for the badger in the. In the cost benefit analysis.

[Tim Harford]

And do you think that that must be wrong, then?

[Stephen Castles]

You think.

[Tim Harford]

I mean, it's a hard question to answer, but you are claiming that the answer can't possibly be zero.

[Chris Cook]

I think the fact that there are people that care about the badger enough, like Brian May, to devote large amounts of their time to campaigning for its survival suggests that the average valuation of a badger's life is probably something above zero. It's probably not a million pounds. A badger. Right. We're not saying they are terribly important. We're not saying also that you could never justify killing a badger. I live in Zone one in London. I'm really the last person to be telling other people what they should be doing with their badgers.

[Stephen Castles]

But the.

[Chris Cook]

It seems very, very unlikely that the correct valuation of a badger's life is zero.

[Tim Harford]

Chris Cook. The value of the marginal badger isn't the only question on the table here. Another big issue for those in the know is how many badgers are actually going to be killed. The government's aim is to kill 70% of badgers in the pilot zones. Now, this stipulation has had protesters reaching for the small print of the Berne Convention, the Council of Europe's treaty on wildlife Protection. Professor Rosie Woodruff of the Zoological Society of London, who was involved in a major controlled trial of badger culling in the past, can see a problem with this target.

[Rosie Woodruff]

To be confident of killing 70% of the badgers in an area, you have to know how many badgers there are. But as it turns out, counting badgers is really difficult. If you want to count some conspicuous animal like elephants or giraffes, you can fly around in an airplane, look out the window and just count how many you see. And babadas only come out at night. They're difficult to see, they all look the same. It takes skill to tell which burrows you see in the field are being used by badgers, which are being used by other animals like foxes and rabbits. And then each family group of badgers is going to be using more than one of those sets. So it's not straightforward to work out how many badgers there are in a particular piece of land.

[Tim Harford]

So let's be specific. How many badgers do we think there are?

[Rosie Woodruff]

So the Government's best estimate of the number of badgers in West Gloucestershire is 3,399. In West Somerset, where culling has already started, is 2,494. But there's a great deal of uncertainty around those numbers. So, for example, the government's only about 60% certain that the true number of badges in that West Somerset area lies between 1,972 and 2,973. So they think there's about.

[Tim Harford]

Between about 2,000 and 3,000.

[Rosie Woodruff]

Between about 2 and 3,000. That's exactly right.

[Tim Harford]

And so it might be possible that you could kill all the badgers, violate the Berne Convention and still not kill enough badgers to satisfy the terms of the Government's rules.

[Rosie Woodruff]

That's exactly right, because killing too few badgers risks making cattle TB worse. What the Government's done is to err on the side of caution. So because in West Somerset, they think there could be nearly 3,000 badgers, Natural England is requiring farmers to kill just over 2,000 of those badgers there. But remember, we're actually not sure how many there are in the area. There's a good chance there may be fewer than 2,000 badgers in that West Somerset area. So farmers are being legally required by their licenses to cull more badgers than actually may be present in the area.

[Tim Harford]

Professor Rosie Woodruff of the Zoological Society of London. You're listening to More or Less with me, Tim Harford. Our email is more or lessbc.co.uk and over the summer break, that email inbox received a number of inquiries asking about a claim in several newspapers that 13,000 people had needlessly died as a result of poor quality care at the worst performing NHS trusts in England. Those headlines were printed days before the publication of Sir Bruce Keogh's review into 14 hospitals, which had been chosen because they had high mortality ratios according to one of two measures. Now, Hannah Barnes is with me.

Well, first up, one of our listeners, Martin Boley, questioned how the 13,000 extra or needless deaths had been calculated in the first place.

And we can definitely help with that one. It all stems from something known as the Hospital Standardised Mortality Ratio, or hsmr, which determined which were included in Sir Bruce's review. But the figure of 13,000 deaths itself doesn't appear in his report.

No, instead, Sir Bruce, who's Medical director for the NHS in England, said that, and I'm quoting now, however tempting it may be, it is clinically meaningless and academically reckless to use such statistical measures to quantify actual numbers of avoidable deaths. And he says that because the HSMR is not a measure of avoidable deaths, or needless deaths, as the papers prefer to call them.

[Mark Elliot]

Right.

[Tim Harford]

The HSMR is the ratio of observed deaths in a hospital to the number of deaths you might expect based on the national average. Using that, you can simply subtract the expected from the observed number of deaths. And that's what happened. Back in July. The Daily Telegraph totted up all those numbers from the 14 trusts being reviewed by Sir Bruce Keogh over a six year period and got the number 13,332.

And the Telegraph got that number and those data from Professor Sir Brian Brian Jarman, who's head of an organisation known as Dr. Foster, which is based at Imperial College in London. He's clear he never said the HSMRs measured needless or avoidable deaths and nobody could responsibly do so here. Professor Jarman quotes from the email he sent the Telegraph, which is now in the public domain.

[Brian Jarman]

What I emphasise in that is that it would be impossible statistically to calculate the precise number of deaths that were unnecessary or to pinpoint which particular incidents were avoidable. That, if it were possible, would require careful consideration of the case notes for individual mortalities themselves.

[Tim Harford]

Couldn't be much clearer, really. But Hannah, there have been more questions.

Robin Proctor asks, is there more to this than a slightly more subtle version of shock headline? 50% of doctors are below average.

And the short answer to that is no. If we can be forgiven for smoothing over a couple of wrinkles, the basic story is we should typically expect about half of NHS trusts to be below average. And that fact should really shock nobody. And in isolation, it tells us very little.

And by the same token, you'll get other hospitals that are above average. A point that's picked up by another more or less listener, Michael Hinson, who says, quite correctly, I presume that there must also be 14 or more hospital trusts with fewer deaths than expected.

So these aren't needless deaths, they're needless lives. A sort of statistical undead walking the streets of Britain when the average hospital would have killed them.

Yeah, it's nonsense. And that's why the HSMR shouldn't be used to infer any number of actual avoidable deaths. But Sir Brian Jarman, who pioneered this statistical device, says that it can be really useful for flagging up problems.

[Brian Jarman]

We actually send a letter to all trusts that have a particularly high mortality for one particular diagnosis or procedure every month. It's what actually triggered the MID staffs inquiry. And we say that this could be due to coding, it could be to the method of adjustment, it could be two or three things, or it could possibly be related to quality of care. And we're just giving you this information so that you can look further and see whether there is a potential problem.

[Tim Harford]

But the story doesn't stop there, because the hospital standardised mortality ratio is actually a controversial matter among the statistically savvy. Nick Black, professor of Health Services Research at the London School of Hygiene and Tropical Medicine, is one of HSMR's fiercest critics. He's previously looked at whether there's any connection between a high standard mortality ratio and a large number of avoidable deaths, and he says there isn't. He's now been asked by the NHS's medical director, Sir Bruce Keogh, to look further at that question and to use the same research to pave the way for the introduction of a new national indicator on avoidable deaths in hospitals. I asked Professor Black what role, if any, HSMRs should play in the future.

[Nick Black]

I'd like to see them scrapped. As H.L. mencken said many years ago that for every complex problem, there is a simple solution and it's wrong. And this is a classic example of that. If I was Secretary of State for Health, I would love the idea that there was a single number that would tell me how my 160 trusts were doing. It's not that simple. Hospitals are incredibly complex organisations.

[Tim Harford]

This is a little disturbing, more or less. We do like numbers and we like to believe that numbers, they're often misused, but they can be wisely used. Is there any administrative or clinical data that would actually tell us something informative about hospitals?

[Nick Black]

Clearly, deaths in hospital are important. The challenge is to come up with an appropriate way, statistically, of looking at that. And the approach that is now being adopted by NHS England and adopted by the government is to look at avoidable deaths. Now, what I mean by that is that in each and every hospital, all the deaths should be looked at by the medical and nursing staff to establish whether or not the patient died from an avoidable problem. Now, we've done that with 10 trusts and what we found was that about 5%, 1 in 20 deaths are avoidable. Our estimate for England, based on the thousand deaths that we looked at, would suggest there's about 12,000 avoidable deaths in adults in acute hospitals in England each year. So what's being advocated and will be put in place from next April, is that all trusts will be expected to review probably 100, 120 deaths in their trust in great detail to establish whether or not the patient died as a result of avoidable causes.

[Tim Harford]

Professor Nick Black. Now, what are we to do with Labour's immigration spokesman, Chris Bryant? It seems that every time he makes a statement at the moment, there'll be a correction along in a minute. Earlier in the summer, he released extracts from a speech taking aim at Tesco and next for recruiting too many immigrants. By the time the speech was delivered, many of his claims had been withdrawn and Mr. Bryant was taking full responsibility. So who's going to take full responsibility for this?

[Nick Black]

So if we get climate change wrong, there is a very real danger we shall see levels of mass migration as yet unparalleled.

[Tim Harford]

That's Chris Bryant in the process of being afraid that millions of people around the world will be forced to flee their homes and, in their droves, move to countries less affected by environmental problems. Some of this, he says, has already happened.

[Nick Black]

The United nations estimates that in 2008, 20 million people were displaced by climate change, compared to 4.6 million by virtue of internal conflict or violence.

[Tim Harford]

But much more is to come.

[Nick Black]

You can imagine that the UN estimates of 200 million such refugees, more than the total number of worldwide migrants today, may be about right.

[Tim Harford]

Now, in fairness to Mr. Bryant, he didn't just make that claim up, it did indeed come from the United Nations. But we still suspect that some kind of retraction may be necessary. Alas, here at More Or Less, we have a climate migration correspondent, Hannah Barnes. Hannah, you've done this before. You specialise in taking the heat out of these kinds of statistics.

That's right. But it's not just me. Various experts in the field and even concerned charities have to spend a lot of their time correcting overblown statements like these.

Let's start with the claim that 20 million people were displaced by climate change in 2008.

And a surprising critic of that number, Alex Randall, works for the Climate Outreach and Information Network, a charity which aims to raise awareness of climate refugees and their needs. So you might think he'd be shouting the same alarming numbers from the rooftops and. But he's not.

[Alex Randall]

What Chris Bryant was quoting in his speech was a kind of adding up all of the people who've been displaced by any kind of natural disaster and labeling them climate refugees. And that's problematic for a number of reasons. Firstly, because the relationship between natural disasters and climate change is complicated. It's certainly true that climate change might be making some of those particular disasters more likely, but it's certainly not the case that we can attribute all of those individual displacements to climate change alone.

[Tim Harford]

And Even if all 20 million people had been displaced by climate change, they're unlikely to be looking to set up home in a new country.

[Alex Randall]

The idea that in the event of a natural disaster, people will immediately move long distances and permanently is mistaken. People tend to move short distances for a short period of time and then move back.

[Tim Harford]

So let's take a look at this claim from the United nations, quoted by Chris Bryant, that 200 million people will become climate refugees in future.

Yeah. And what we're really talking about here is people who have to leave their homes because their lives and livelihoods are being adversely affected by climate change. So not just because of sudden natural disasters, but because of a slow creep, changing weather systems, say, or rising sea levels. But many experts don't expect this to cause mass migration. Alex Randall explains why.

[Alex Randall]

If it becomes increasingly difficult for a farming community to sustain their livelihood by growing the crops that they have been, what's likely to happen is that in response to that, rather than all of them at once upping sticks and moving to another country, the likely response is that one or two household members will move, probably within their own country and probably to a big urban centre, to a city nearby. They'll then work and send money back to their family.

[Tim Harford]

So migration tends to be relatively local and small scale. Now, I was fascinated by the way the UN justifies its claim that 200 million people will become climate refugees.

It doesn't. The UN told me it cannot comment in any way on the accuracy of a figure we did not produce.

So they're happy to use the figure, just not to defend it.

Quite. Now, the figure is the work of a scientist called Norman Myers, who's based in Oxford in the uk.

Now, we've heard about his work in the past.

Yep. Back in 2011, we looked at his claim that 50 million people would become climate refugees by 2010. It had been quoted by some influential institutions, but one year on, there was scant evidence that these people existed. The UN had a map showing this prediction on the website, but hastily took it down. We discovered when it started to get attention initially, clearly there was no explanation as to why it had disappeared. Just a totally bizarre message came up when you went to click on the link.

[Stephen Castles]

Dear Visitor. It seems like the map you're navigating by is maybe not fully up to

[Tim Harford]

date or that it might have an error in it. Or is it that your GPS is not loaded with the correct data? We're just taking the scenic route, darling.

[Stephen Castles]

See, honey, we're not lost. I know where we are. This way, I think.

[Norman Myers]

Hmm.

[Tim Harford]

I love it when our investigations take a surreal turn.

Well, eventually the fog lifted and a spokesman for the United Nations Environment Programme told me the map had been removed because it was wrong.

They had funded the research it was based on, though.

They had. And this work had been unquestioningly adopted by all sorts of eminent bodies like the Intergovernmental Panel on Climate Change. But some academics had doubted his numbers from the start. Stephen Castles from the International Migration Institute at Oxford University outlined some of his concerns to me at the time.

[Stephen Castles]

Norman Myers, who I know we've discussed together, is an environmentalist. And I think his objective in putting forward these dramatic projections was to really scare public opinion and politicians into taking action on climate change, which, of course, is a very laudable motive. But the problem was that he really used a method to make projections that is really not permissible at all. He simply took a map of the world, worked out what areas would be inundated if the sea rose, say, by 50 centimeters, and then simply assumed that all the people affected by this sea level rise would have to migrate and that a lot of them would migrate to developed countries. And really there was no basis for it.

[Tim Harford]

And the 200 million figure was calculated in the same way?

Yes. It's his projection for the number of climate refugees there'll be by 2050.

So he said 50 million by 2010 and 200 million by the time climate change takes hold.

Yes. And he defended his methods to us at the time.

[Norman Myers]

It's very difficult to say how many there are and where are they, and to point out to a crowd over there on the horizon and say those are environmental refugees, it is difficult. I would not like to be the person who tries to come up with an exact, precise figure. But in the long run, I do believe very strongly that it will be better for us to find we have been roughly right than precisely wrong. I would be very suspicious of somebody who said, where are they? I think it would be much harder to demonstrate that there aren't any of these environmental refugees than to demonstrate that there are environmental refugees.

[Tim Harford]

But if you can't prove that there are, then we shouldn't be making the statement, should we? We can't prove it.

[Norman Myers]

Well, you can't prove that smoking causes cancer. Science is never, never, ever completely final. It's always a bit iffy.

[Tim Harford]

Iffy, good choice of word.

Well, to be fair to Norman Myers, he did make it clear in his research that not everyone he classes as an environmental refugee will flee their country. He just said that they'll be forced to move and that could well be

internally and equally, Stephen Castles didn't deny that some people have been and will be forced to move country.

[Stephen Castles]

We do have some cases where places have become or are likely to become uninhabitable. There are these very small Pacific islands like Tuvalu and Kiribati. But of course the populations there are very small. We're talking about a few thousand people, ten thousand at the very most there. One would say migration to New Zealand or Australia might be the long term solution for at least some of those people.

[Tim Harford]

But that's tens of thousands, not tens of millions.

[Stephen Castles]

Absolutely, yes.

[Tim Harford]

Stephen Castles from Oxford University's International Migration Institute, who back in 2011 was talking to Hannah Barnes. One thing, Hannah, I thought you were our COD correspondent.

I am, I am. It's just a bit quiet on the COD news front at the moment.

You're listening to More or Less with me, Tim Harford. Our email address so you can report all manner of statistical curiosities is more or lessbc.co.uk now all loyal more or less listeners like data. And if you like data, you're going to love big data. It's like data, only bigger. And the phrase is currently being used to flog management books, speeches and consultancy services to companies around the globe. But while big data is fashionable, what exactly is it? Mark Elliot at Manchester University advises companies how to handle their datasets. So I thought he was the man to ask.

[Mark Elliot]

One of the problems is that big data is a misnomer. It's a bad term for what we're trying to talk about. The main interesting feature of the data is not its bigness. The main features of big data in its current form that are interesting and will have huge impacts on us are the fact that it's real time data and that it's linked data. So this is data that is combined across a whole different set of different pieces of information. And it's also data that's being used as it's being collected, for example, health monitoring data.

[Tim Harford]

So this is what, an Internet enabled pacemaker or a smart toilet that analyses your poo?

[Mark Elliot]

Or it could be any of these things. We're looking at things that can take Your temperature things take your blood pressure in real time, blood sugar levels. Any of these things in principle could be monitored and indeed it could be actual ordinary devices in your own home that have these sensors in them. It needn't be something that's plated to your body. But one way we could go is a much more tighter linking of data to protein. For example, one can imagine the government introducing a new policy where benefits were cut, just as in fact has just happened. Now there's claims made from various parties about the impact that's going to have on what food people buy. They either pay their rent or they eat healthily. Well, if we were linking that policy instrument to the benefits income instrument and supermarket data, we could actually see what the impact was on people's diets. So we could have a direct relationship and analyze between what people were paid in benefits and the impact that had on what they ate in terms of whether they were getting enough vitamins and minerals and so on.

[Tim Harford]

Mark Elliot Every one of us is already producing lots of data which researchers and big corporations can use. For instance, if you have a mobile phone, your phone company knows a lot about where you are at any moment. If they didn't, they wouldn't be able to route calls to you. So phone companies can and do package up all this data, strip out the personal information and sell it, for instance, to a retailer who wants to know whether a particular location will get a lot of passing trade. It's a good job this data is anonymous, after all. Imagine if your partner realised that your mobile phone occasionally seemed to spend the night snuggled up with an old Flames mobile phone in a motel near Basingstoke. That could be awkward. But what if the anonymous data releases aren't really anonymous? What if little clues could allow your identity to be deduced from the data in question? I've been talking to Ed Felton, professor of Computer Science at Public affairs at Princeton University. I began by asking him how a rogue agent goes about de anonymizing a data set.

[Ed Felton]

There are different methods. In all cases, it involves assembling small pieces of data from different sources and putting them together to make a kind of mosaic from which an identity emerges.

[Tim Harford]

So when we're told that a data set has been released and it's been anonymized, I mean, should we just always conclude that that statement is false?

[Ed Felton]

It is possible to anonymize or clean data sets so that they are safe to release, but the difficulty is it can be very hard to tell whether you've done that successfully. And we're just now starting to see the emergence of a sort of science of anonymization and de. Anonymization, so that we can know with mathematical confidence that a particular data set might be safe.

[Tim Harford]

Here's an example of how this potential problem can become reality.

[Ed Felton]

Well, let's tell the story about Netflix. Netflix is a service that sells people movies, and they want to be able to recommend movies that you're likely to like. And a few years back, Netflix issued a challenge to the public to try to help them improve their prediction or recommendation methods. And the way they did this is they took a bunch of data about what their real users did and liked, and they scrubbed the names and user identifiers out of that information and then they released it. Well, some researchers took that data and what they showed was that it was possible in many cases to identify which users had corresponded to which records by combining the data set with external data sets. For example, IMDb, which is a site that publishes information about movies. And some users of the IMDb site corresponded to users in the Netflix data set.

[Tim Harford]

They could figure out that this particular person who had rated or reviewed movies on IMDb with their real name. You could also see all their Netflix downloads and orders.

[Ed Felton]

That's right.

[Tim Harford]

I understand there was a woman who alleged that it was possible to out her as a lesbian on the basis of the reviews she'd written and the movies that she'd rented. And so what appears to be very innocent data could actually be revealing very, very personal facts about people. Do you think we are getting a good deal in this Whole Big Data vs Privacy Trade Off?

[Ed Felton]

For the most part, citizens making decisions about their data practices and what to allow are not thinking carefully about what they are able to do. And companies are not very transparent about their practices. I think we could do better than we are simply by more transparency and a more honest conversation about what we're giving and what we're getting.

[Tim Harford]

Ed Felton from Princeton University. If there's a number you'd like us to investigate or just prod a bit, email us at more or lessbbc.co.uk. you can get our download freebie at our website, BBC.co.uk more or less so you can have me in your pocket wherever you go. This week's episode of More or Less was brought to you by the Number one. Until next week, goodbye.

More or Less was presented by Tim Harford, the Financial Times undercover economist. It was produced by Ruth Alexander and made in association with the Open University. You can download many more Radio 4 programs for free. Find [e-mail] Radio 4.