Asthma, Visual snow, Confounding factors

Why asthma is both over diagnosed and undertreated. Professor Mike Thomas and GP Dr Margaret McCartney discuss this apparent contradiction and look behind recent headlines that half a million children in the UK could be taking asthma medicines they don't need. A new study finds that putting doctors under pressure or being a difficult patient may backfire, inducing them to make diagnostic errors. With scarlet fever and measles in the news, Margaret McCartney gives a quick guide on the key symptoms as both diseases have a characteristic rash. A listener has emailed to ask about visual snow, a condition where your vision is like an untuned TV set. World expert, Professor Peter Goadsby explains the latest understanding of visual snow, and says that even 15 years ago it hadn't been universally accepted as a condition. Plus the first in the latest Inside Language series with Margaret and Dr Carl Heneghan of Oxford University. This week, they discuss confounding factors and why they matter to your health.

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28 minutes

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Tue 15 Mar 2016 21:00

Programme Transcript - Inside Health

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THE ATTACHED TRANSCRIPT WAS TYPED FROM A RECORDING AND NOT COPIED FROM AN ORIGINAL SCRIPT.  BECAUSE OF THE RISK OF MISHEARING AND THE DIFFICULTY IN SOME CASES OF IDENTIFYING INDIVIDUAL SPEAKERS, THE BBC CANNOT VOUCH FOR ITS COMPLETE ACCURACY.

 

 

INSIDE HEALTH

 

Programme 10. – Asthma, Visual snow, Confounding factors

 

TX:  15.03.16  2100-2130

 

PRESENTER:  MARK PORTER

 

PRODUCER:  ERIKA WRIGHT

 

 

Porter

Coming up today:  Pushy patients – why putting your doctor under pressure may be bad for both of you.

 

Visual snow – imagine if your world looked like the screen of an old out-of-tune TV.

 

Clip

We’re looking at the picture that a young girl, 12-year-old, drew for us.  She came in to see us with visual snow problem and we were interested in her showing us what happened.  So she’s drawn a house that’s got nice windows in it with a brown tree with some greenery on it.  And she’s drawn a whole lot of squiggles in black all over the sky and all over her visual field and you can see them almost moving about.  And what she’s showing us is that her vision, whilst she can see things, is constantly disturbed.

 

Porter

And our Inside Language series returns to demystify the terms used by those publishing and reporting clinical trials. This week it’s all about confounding factors.

 

But first asthma and recent headlines claiming that half of all children diagnosed with the condition might not actually have it. The coverage was prompted by a Dutch study that tested lung function in 650 children labelled with asthma. Just over half had normal spirometry, suggesting they did not have the condition. A proportion that if extrapolated to the UK could mean hundreds of thousands of children here are taking asthma medicines that they don’t need.

 

The National Institute for Health and Care Excellence is currently reviewing its guidance on asthma and will be updating advice to improve the accuracy of diagnosis. One of the experts advising NICE is Mike Thomas, Professor of Primary Care Research at the University of Southampton. So do the Dutch findings reflect what is likely to be happening here?

 

Thomas

I think Mark the evidence is that as with the rest of the world we’ve got simultaneous over and under diagnosis going on, which it sounds a bit contradictory but I think there are people who generally do have asthma and have symptoms who aren't getting a diagnosis and aren’t getting effective treatment.  But then there may well be people who have other respiratory conditions that are causing similar types of symptoms who are getting a label of asthma and so are receiving treatment that isn’t helping them much.

 

Porter

Does that matter?  I mean is it inevitable that we’ll encompass some people may be who’ve just got a bit of viral induced wheeze for instance into that diagnosis?

 

Thomas

Well I think it does matter Mark because the mainstay of treatment for asthma is with inhaled steroids and many patients and in particular many parents of wheezy children feel a bit uncomfortable about giving long term treatment with inhaled steroids unless it’s absolutely necessary.  And the evidence is that maybe some people who receive a diagnosis don’t actually benefit from inhaled steroids.  So I mean in a way the way we’re going in asthma is that it’s not just one condition, one diagnosis, it’s a bit like when we say somebody’s got anaemia, there are lots of different causes of anaemia and everybody who wheezes or gets respiratory symptoms these days tends to get a diagnosis of asthma and then gets treated in much the same way.  And I think increasing sophistication about the drivers of symptoms and the different kind of biological processes going on in people and improvements in technology are leading us now to be able to differentiate who will actually benefit from different types of treatment.

 

Porter

Margaret McCartney is listening in our Glasgow studio.  Margaret, I mean you’re working at the coal face, you’re seeing children, particularly, brought in by worried parents, do you find it hard to diagnose asthma?

 

McCartney

It can be very difficult but equally it can also be quite straightforward.  So if a child comes in they’ve got a very good description of having serial asthma attacks in relationship, particularly, to something that might be happening, for example being in contact with a cat or a pet or something like that that’s triggering if off, maybe their parents or a sibling also has asthma.  In that kind of situation it’s much more easy, especially if a child gets older and has still got symptoms.  But in a younger child the big problem is that viral wheeze is very common in this group of children as well and viral wheeze tends to be caused by a virus but it also gives that wheeziness that is also associated with asthma.  And sorting out the two of them can sometimes be quite straightforward but sometimes can be a bit more difficult.  In the Dutch study, the study from the Netherlands, that had found over diagnosis of asthma I think there’s an awful lot of uncertainty.  And I think part of the problem is the way that doctors tend to work in putting a code in children’s notes and I think sometimes the code can be wrong but it might have been right at the time when it was placed on there, it might have seemed that there was an asthma type scenario going on but maybe two or three, four years later that’s no longer the case, the child has hardly needed to use the inhaler, the symptoms have got much better.

 

Porter

Mike, I’m intrigued by this over diagnosis.  I mean actually looking at my practice I could suspect that, if anything, we might come in under the required number because sometimes when we’re not sure whether a child has asthma or not we’re not coding them as such, we’re just giving them the benefit of the doubt and watching them, particularly the younger children.

 

Thomas

I think we have got a slightly messy situation at the moment Mark.  I mean I think generally GPs have been receiving this message from specialist care over the last 10 years or so that we’re under diagnosing asthma, so there’s almost like this pressure to make a diagnosis of asthma on children who have recurrent respiratory symptoms and while it is important that people don’t miss out on having effective treatment, I mean giving a diagnosis for asthma is quite a big deal, it has implications for that child and the family, it has implications for sport, for insurance, for long term life plans and so on.  And I think we need to be pretty sure before we give a definite diagnosis of asthma and I think the concept of giving a diagnosis of suspected asthma is very reasonable because we don’t have a simple yes or no test because the trouble is that once the diagnosis gets applied – if somebody gets given a treatment and then they come back because the treatment isn’t working what tends to happen is rather than review of the diagnosis there tends to be an escalation of the treatment, so they get given higher doses or more types of treatment that may be they’re not responding to.

 

McCartney

I definitely agree with that and I think there is a room for uncertainty around this area.  But part of the reason why these codes are put on people’s notes is so they can be recalled for regular review.  So I think the intention has been generally good but the unintended hazard has been that then sticks with the patient, whereas it might be better off actually being reviewed.  And I think it is a difficulty of these kind of binary codes that we put on people’s notes, is that really the best thing to have a permanent label where actually the situation must be quite a lot more fluid.

 

Porter

How do we improve the diagnosis?  One of the techniques that’s being highlighted is the use of spirometry, a special lung function test that can be done in general practice.  How accurate is that though in diagnosing asthma?

 

Thomas

Well spirometry is a very good way of showing whether there is some narrowing of the air tubes, so it’s a very good objective demonstrator that somebody does have abnormal airways function.  And if you get a positive result from spirometry, i.e. if you show that the tubes are narrowed and then you give something to relax the muscles in the airways and the lung function improves, that’s very good evidence that somebody does have asthma.  However, a negative test doesn’t rule asthma out because asthma can be quite an intermittent condition and if you’re not actually exposed to a trigger at that time you may have normal lung function.  But there are other types of tests that we can add in to spirometry, such as exhaled nitric oxide, which again is a simple near patient test where a patient blows into a machine and this tells us how inflamed people’s lungs are and it’s the inflammation in the lungs that’s controlled by steroids.  So it’s quite a good guide to who will benefit from an inhaled steroid.  And some of the people who have a diagnosis of asthma at the moment don’t have evidence of inflamed airways, so it’s very uncertain about whether they’re actually getting much benefit from the steroids.

 

Porter

Could it be though with children that there might be a sub-group of people who have relatively normal lung function when you test them on a spirometer and indeed normal signs of inflammation using other more complex measurements because symptomatically they’re well, they have a milder condition but in the winter after a viral illness they really can be quite poorly?

 

Thomas

Yeah that’s definitely true Mark and that is one of the issues about asthma which it is an intermittent condition that normal results at a single moment in time don’t mean that they don’t have asthma.  The test for airways inflammation are a bit more specific because if you have symptoms and evidence of inflammation then the evidence we have at the moment is that you’re much more likely to respond to treatment.  And indeed NICE, who’ve reviewed the evidence, NICE recommended that everybody with suspected asthma from children from five years upwards should have quality assured spirometry and exhaled nitric oxide.  Now there are very significant service delivery and commissioning implications to that because it does mean that GPs would have to have access to tests that currently they don’t have access to.  So at the moment rather than launch the guideline NICE is initiating a series of pilot studies in selected practices where they’ll provide equipment and training to the staff to see will it actually result in better diagnosis and will it be able to be integrated into routine general practice.

 

Porter

And we shall await the results of those pilots with interest. Professor Mike Thomas thank you very much.

 

Now Margaret, conventional NHS wisdom has it that the squeaky wheel gets the grease – the more a patient pushes the more likely they are to get what they want. But new research suggests being pushy could be bad for your health. What did the study show Margaret?

 

McCartney

Essentially being demanding and threatening doesn’t tend to result in better healthcare. This was a study that was done with doctors in the Netherlands and the doctors were given written clinical cases, so not real life, with a set of circumstances with symptoms that patients described, test results the patients had but importantly the kind of consultations that the doctors had with these fictitious patients.  Half the time it was completely neutral, it was just about information exchange, the other half the doctors were told that the patient was demanding, threatening or accusing the doctor of incompetence of something going badly wrong.  And essentially what they found was that the more unpleasant the consultation was the less likely the doctors were to make the correct diagnosis.

 

Porter

Which goes against this sort of general cultural belief that’s out there at the moment that the pushier you are the more you get and the better you do.

 

McCartney

Yeah and I’ve seen this on lots of websites, advising you how best to interact with the NHS, which often advises people to tell the doctor what you want and then you’ll get it.  But the problem is, I think, that healthcare is not always a kind of exchange like that and if you don’t get the correct diagnosis then obviously nothing much else is going to make sense after that because that’s the most important thing – to know what you’re actually dealing with.  Now there are lots of flaws we could point at about this study – these doctors were relatively junior, it wasn’t real life – however healthcare is a very human act and it’s difficult enough to get things right, never mind creating circumstances that make it more likely for us to get things wrong.

 

Porter

And that was the key here – the doctors weren’t balking at the patient’s attitude, it’s just that – it was just taking their eye off the ball effectively.

 

McCartney

That’s exactly what these researchers suggested.  And what they suggested was that you’ve got a limited supply of mental capacity per consultation and if we’re using that all up on how to diffuse a tense problem or how to try and stop someone complaining about you then you’re not using that in order to make the best diagnosis.  Now healthcare’s often stressful, it’s often very difficult when you’re ill, when you’re worried about what’s going on, when you’re scared of what’s happening to you and I think we all would want to forgive people who maybe say things or do things that in retrospect they would rather not have done.  And I think it’s useful for doctors to know that when we are caught up with trying to deal with a tense situation we might have to think extra carefully about what actually the diagnosis is.  But I think it’s really interesting.  In general if you go in with a combative attitude let’s not be surprised when things perhaps don’t work out as optimally as they could.

 

Porter

Indeed, actually my advice would be to be persistent if you’re concerned, rather than pushy.  But then again Margaret we both have obvious vested interests.

 

Now two old adversaries have also been making the headlines. There have been 20 cases of measles in the South East of England, and the number of children developing scarlet fever is at a 50 year high with around 600 new cases a week in England alone. Parents are being urged to make sure children are up-to-date with the MMR jabs, and to be aware of the symptoms of both measles and scarlet fever. Well we can’t help with the MMR Margaret, but we can spell out the differences twixt the two – both of which are associated with characteristic rashes.

 

McCartney

They are and I have to say I have never actually seen a measles rash, that’s how rare it is, even though we have these outbreaks, it’s still largely prevented by our MMR vaccine.  So there are two distinct illnesses – scarlet fever tends to cause sore throat, a fever, a headache, a pinkish rash that often feels quite sandpapery when you run your fingers over the torso of the child, might itch, they classically get this red strawberry tongue and at the end of the illness sometimes their skin on their fingers and toes will peel off and the rash tends to occur a couple of days after the symptoms and we usually treat that with penicillin.  Whereas measles tends to be coryzal symptoms – runny nose, a cough, sneezing, eyes will hurt in the light, often a bit swollen, a temperature, koplik spots, they’re called, in the mouth little kind of whitish grey spots sometimes.  And you tend to get the rash a few days after the symptoms appear.  It’s usually on the face, underneath the hairline, usually then spreads over to the neck, the trunk, the arms, legs, sometimes also the feet as well.  Quite often you get little raised bumps on top of the flatter redder spots but Mark I’ve never actually seen measles, I’m getting all this information from textbooks.

 

Porter

Well it’s been years since I have Margaret and that really sums up how rare it is isn’t it?

 

McCartney

Yeah absolutely, even though we’re hearing a lot about it just now it is overall rare.

 

Porter

Thank you Margaret.  And as ever there is more information on the Inside Health page of the Radio 4 website; including a link to the pushy patient study.

 

Now, please don’t adjust your sets.

 

TV snow sounds

 

An out of tune telly, which is how listener Aaron describes his vision – and it’s been that way for as long as he can remember. Why, he asks in an email, has the symptom proved so challenging for his doctors, and has any progress been made in treating the problem?

 

Well it sounds like a complaint known as visual snow. If so Aaron is far from alone as I discovered when I met world authority on the subject – Peter Goadsby, he’s Professor of Neurology and Director of the National Institute for Health Research Wellcome Trust facility at King’s College London.  And he’s seen over a thousand patients with the same disturbance of vision.

 

Goadsby

So a patient with visual snow sees a constant myriad of dots that they very often describe like an old television, analogue television, that’s not tuned.  And those of us of a certain age will understand immediately what that means…

 

Porter

I do.

 

Goadsby

Exactly and those who don’t could google it and see.  And if you show it to a younger person with visual snow what that is they’ll almost cry, they’ll just say yes that’s what this looks like.  This is constant and on a, for example, at night against a black background they’ll see a myriad of white dots moving all about the visual field.  And on a white background during the day they’ll see a myriad of black dots moving.  Now some of them will see coloured dots and some have some clear ones but the broadness of this is this snow appearance.

 

Porter

You’ve brought an interesting picture with you, is this one of your patients?

 

Goadsby

It was.  We’re looking at the picture that a young girl, 12-year-old, drew for us.  She came in to see us with visual snow problem and we were interested in her showing us what happens.  So she’s drawn a house, that’s got nice windows in it, with a brown tree with some greenery on it and she’s drawn a whole lot of squiggles in black all over the sky and all over her visual field.  And you can see them almost moving about.  And what she’s showing us is that her vision, whilst she can see things, is constantly disturbed.

 

Porter

And what’s the typical story – is there a typical story?

 

Goadsby

There’s two typical stories you might say because there are people who’ve had it since birth, about a quarter of the patients we’ve seen have had it as long as they can remember.  And there’s a realisation point where they sort of say to someone - don’t you see that.  A good example, we were doing the research and one of my clinical fellows after we’d talked to about a dozen people or so forth pulled me aside and said doesn’t everyone see that.  No.  Well I do.  It hadn’t occurred to them, because they never asked anybody, that everyone doesn’t see like that. And the other three quarters of people have it come on at some point in their life.  Various things will happen and it’ll flick on.

 

Porter

Is it the same underlying mechanism that’s responsible in both those cases because that’s quite different isn’t it?

 

Goadsby

This is at such an early phase – 15 years ago we wouldn’t have had the discussion, no one would have agreed on what we were talking about.  But I’ve seen a seven year old with this, I’ve seen a 70 year old, I’ve seen people in North America, seen people in the UK, I’ve seen people describe it in India, Australia and in China, they describe the same thing.  What that said to me is there’s a shared biology here and it’s turned on in a different way but there must be a common pathway. 

 

Porter

But a pathway we don’t yet understand?

 

Goadsby

The journey that’s happened is if a patient has an eye problem what do they do – they might see an eye doctor, do all sorts of tests and they’ll shine lights and they’ll say you’re normal.  Then they might get referred to a neurologist, because – well the eyes are connected to the brain, so let’s talk to the brain doctors.  And the brain doctors will go – the brain’s normal – then do a scan and examine them and that’s all fine and dandy.  And then unfortunately some patients, the next level is to go to the psychiatrist after that because when the brain doesn’t work it must be psychiatric.  Now I got involved because as a headache/migraine person I’m used to the idea that you can have a flashing visual disturbance that’s very troublesome and it can be disabling and it’s completely normal afterwards and your brain looks normal.  So I was sent these patients.  What they describe is nothing like migraine aura. 

 

Porter

What’s the natural history of this, if someone comes to see you, I mean let’s look at the larger group – that have had a sudden onset following some form of event – they come and see you two or three years later, I mean can you say this is going to get better?

 

Goadsby

I can say one thing that’s almost certainly true – you’ll never lose your vision.  It seems to stabilise.  We don’t know enough about the natural history yet.  In the generality of things I think it waxes and wanes, from a therapeutic perspective, and we know some things that you shouldn’t do, for example, one of the most obvious examples a hallucinogenic, LSD like drugs, can produce a similar thing, it used to be thought that everyone with this problem must have had an hallucinogenic drug.  The first time I saw a seven year old with the problem I thought yeah, no, okay push the button.  I’ve seen literally and discussed this with hundreds of patients who haven’t done that, but we tell them to avoid that sort of thing, which is recreational drugs is a bad idea.  Therapeutically we’re in a difficult place because we don’t understand the physiology.  We have a little bit of an idea.  We’ve found an area in the back part of the brain, which is the vision part of the brain, and a particular structure at the back part of the brain that’s more metabolically active, more blood flow, in visual snow sufferers than in controls.  So we’re sort of narrowing it down so that either that part of the brain is not turned down enough, inhibited as we say, or it’s too excited.  And when we understand that through the sort of research I’m talking about we’re going to know which direction to go.  I mean it’s pretty exciting to be into something where in 2001 embarrassingly enough I was seeing these patients and just sort of thinking I’m not sure what’s going on, to a point where we’ve got a description that’s accepted, we published it in a journal called Brain which is a bit – well it’s to cricket is what Wisden is to neurologists, Brain is just one of the great journals of neurology.  So when you publish something it validates things in a way that’s useful, you know yourself from your practice simply giving an assignment to the problem, to say I understand you’re not crazy, no more than me, and I understand that there’s a serious problem for you, it’s disabling, that’s useful in a way that’s quite important.

 

Porter

Professor Peter Goadsby on the unusual symptom of visual snow.

 

Claudia Hammond from All in The Mind has popped in to the studio to remind us all about The Rest Test – explain all Claudia.

 

Hammond

Well this is the world’s biggest ever survey on rest that we’ve been running on All in the Mind and already 20,000 people from around the world have filled it in and there are just two weeks more for people to fill it in if they want to.

 

Porter

And what does filling in involve?

 

Hammond

So there are two parts to it.  In the first part we ask what you think rest is, what sort of activities you think are restful – it might be lying down, for one person, it might be taking a run or going swimming for another person, they may feel that their mind can’t rest until they do something like that.  And whether you get enough rest and what your working hours and so on and all sorts of other information.  In the second part we look at more detailed questionnaires about how much your mind wanders, about your personality and about your health and wellbeing.  And then we’re going to put all these together and look and see what we can say about the nation’s resting habits.

 

Porter

And if Inside Health listeners want to fill in this form how do they do it?

 

Hammond

What they need to do is to go to resttest.org and they can fill it in there, the whole thing takes about half an hour-ish, depending on how quickly you do it and we really want to know what people think about rest.

 

Porter

Is it anonymous?

 

Hammond

It is, it’s absolutely confidential and nobody will ever know what they said so people can say whatever they like.

 

Porter

Thank you Claudia.

 

Now it’s time for the return of our Inside Language series which demystifies the terms used by researchers and statisticians in trials and studies. This week Margaret McCartney teams up again with Carl Heneghan, Professor of Evidence Based Medicine at the University of Oxford, to discuss confounding factors and why they should matter to you.

 

McCartney

Confounding factors are one of those things which just drive me crazy.  And the reason for that is that it’s a type of confusion that can result, when you’re trying to work out what’s going on in a clinical trial.  And at the bottom line we’re trying to work out whether one thing causes another thing but we actually find out that it’s something else completely.  So let me give you an example about that.  Say you want to work out whether alcohol affects heart disease.  You might think that people who drink more result in having more heart disease.  But supposing you also find out that people who drink more alcohol smoke more, it’s the smoking that’s the bigger factor for causing heart disease rather than the alcohol.  That’s a kind of confounding I mean.  Another example is for years it was thought that if you were the third, fourth or fifth child born to a mother you had an increased risk of having Down’s syndrome and it was thought for years that the birth order was what caused Down’s syndrome.  And then they realised that actually it’s maternal age that increases the risk of Down’s syndrome, it just so happens that older mothers tend to be having their third, fourth and fifth child.  And that’s where the risk is, it was maternal age not in order of birth, that ended up being the confounding factor.

 

Porter

Carl, how much of a struggle is it to identify possible confounding factors?

 

Heneghan

Well it shouldn’t be a struggle for people to consider them all the time because they virtually exist in all areas when we’re thinking about risk.  And so the problem is is when you try to rule them out or get rid of them and make a statement that says, for instance, chocolate causes cancer or chocolate causes dementia or something can reduce your risk.  It’s very difficult to make that statement.  And as a rule I always say that confounding is always present and you can never rule it out.  And I give you a good practical example that I read the other day, going back to World War II.  We were very interested at the time whether putting fighter planes up in the sky actually reduced the accuracy of the German bombers.  And what we found is the exact opposite – when the fighter plane was in the sky actually the German bombers became more accurate.  And people couldn’t work out why that occurred.  And this is a good party trick if you want to have a good question for people to answer.  The reason was actually it was to do with cloud cover because the fighter planes couldn’t actually go in the skies when the clouds were there and that’s what you call a confounder.  And they tend to be there all the time.  And they’re very hard to adjust for or get rid of.

 

Porter

Margaret, the authors of a paper have a responsibility therefore to identify what confounding factors they can.  But I suppose it rather detracts often from the coverage that they get for that paper as well if they try and explain it away too much.

 

McCartney

Yes, the classic situation is where you have these big cohort studies and you ask people what they eat or drink 20, 30 or 40 years ago and you find some common element in diet that seems to increase the risk of some particular bad outcome.  And then the headlines in the newspapers are of the kind that Carl was saying – chocolate causes cancer, fizzy drinks do this.  So there’s lots and lots of conclusions that could be drawn but of course we have big confounders and the problem very often is that if you’re already healthy in other parts of your lifestyle your diet is very likely to be more healthy as well.  And what ends up as being as individual food factors are discussed as the risk whereas they’re actually a confounder.  And the problem is we don’t really have very good quality control quite often in the headlines, it doesn’t make it clear what’s an association, first of all, rather than a causation and then what could possibly be a confounding factor.

 

Heneghan

Some things are very notoriously difficult to measure.  Nutrition, food intake, is very difficult.  So if you ask me what I’m eating today and follow me up in 10 years’ time how reliable is that a measure of my nutrition over the long period?  Whereas some things like smoking are much more easier to quantify and be objective.  So I’m always very cautious about anything that comes out in a nutritional status and says x causes y and I always revert back to the point this is likely to be an association.

 

McCartney

One of the big examples from years ago was the original trials of hormone replacement therapy and they initially showed that women taking HRT were less likely to get coronary artery disease but actually that’s a confounding going on there because the women at that time who were taking more HRT were very health aware, were reading all the latest literature in magazines about it, they were already a very, very healthy group and it was confounded by the fact that these women were generally more healthy than when it was later rolled out into more randomised control trials and we found that that same protective effect did not exist.

 

Heneghan

It’s a good point Margaret because this happens a lot with supplements, vitamins and I’d love to think I could go out there and take some supplement and that would improve my heart disease risk or extend my life and longevity.  But you always find in observational studies these treatments, supplements, have an effect and that generally is because of the confounding variable of the healthy lifestyle, people who are healthier tend to take supplements.  When they’re subjected to randomised trials, which you then get rid of the confounding, you often find there’s no effect or a very small effect that doesn’t make a difference to you in terms of your longevity or your risk of heart disease.

 

Porter

But if the influence of confounding factors is that well recognised can we not allow for it somehow?

 

Heneghan

Well they are important Mark, confounding factors, but what we have to use then is a statistical technique called adjustment to allow for them.

 

Porter

Professor Carl Heneghan and Dr Margaret McCartney – and adjusting for confounding factors is the topic for next week. When I will also be asking why the uptake for the national bowel cancer screening programme has been so poor. What - besides the obvious – is putting people off? And can anything be done to improve matters. Join me then to find out.

 

ENDS