Of all the animals of prey, man is the only sociable one.
Every one of us preys upon his neighbour, and yet we herd together.
The Beggar's Opera: John Gay

Monday, 9 May 2011

Statistical idiocy in the NHS


All cats have whiskers.
This animal has whiskers.
ergo This animal is a cat.
Discuss

A classic false syllogism? Obviously untrue? Flawed logic? Well not, it seems, for some health professionals in Britain, if the experience of some of my friends and family is anything to go by.

And it can only get worse, to judge from this report concerning breast cancer:

A new report says that as many as 20,000 British women could avoid developing the potentially fatal disease each year, if they took more exercise, drank less and ate better.

So far I have no problem with this per se; I am prepared to agree that they have established links between breast cancer and obesity or lack of exercise and that somewhere between 0 and 20,000 women could avoid developing the disease by a change of lifestyle.

However, that’s not the end of the story: according to the Deputy Head of Science at the World Cancer Research Fund,

“It is very worrying that in the UK there are still tens of thousands of cases of breast cancer which could be prevented every year. Breast cancer can be prevented by cutting down on drinking, being more physically active and carrying less body fat.”

What she means is that breast cancer in cases where it is related to lifestyle can be prevented by a change of habits and losing weight – that is, by the WCRF’s own estimation, about 42% of cases overall.

The other 58% of cases may be linked to environmental or genetic factors or other causes not yet established. Information like this, however, proves a logical step too far for many NHS staff, for whom the mantra runs thus:

Cancer is caused by unhealthy lifestyles.
You have cancer.
ergo You have an unhealthy lifestyle.

In the past few years, several of my friends and family have been diagnosed with so-called ‘lifestyle cancers’, and, to a man (and woman) subjected to lengthy instruction by medical staff about their supposedly unhealthy habits despite a clear family history of the disease in each case.

Thus a friend who walks several miles every day was advised to take more exercise; a non-drinker was repeatedly told to cut down on his alcohol consumption and, most bizarrely of all, a woman who has the healthiest diet I know of was constantly lectured on cutting down on fat and sugar and avoiding junk food – she weighs less than eight stone.

And each of these reported, with varying degrees of fury, a clear and consistent implication by hospital staff that they must have brought the cancer on themselves by their own failure to lead a healthy lifestyle. Their remonstrations were brushed aside - the cancer was proof enough.

It is no secret that doctors receive a ridiculously small amount of training in the interpretation of statistics, given the relevance of probabilities and incidence – I have mentioned before the GP who excused his diagnostic failure with the words, ‘97% of people with this cancer are obese; you aren’t even overweight, so there was only a 3% chance of you having it.’

That being so, how likely is it that the lower echelons of the medical hierarchy can correctly interpret statistical information, given the standard of maths in today's schools? It is a matter of record that numeracy skills are at a frighteningly low level across the population, and I doubt that hospital staff are any exception.

Tell them that cancer is linked to poor diet and lack of exercise and, unless it is clearly explained, some, at least, are going to go on with complete self-assurance to tell cancer patients that it is all their own fault.

4 comments:

  1. Aren't some medications supposed to carry a risk of cancer?

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  2. Very true, Demtrius, and one of them is combined HRT which, like statins, is now being widely prescribed as a matter of routine.

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  3. Neat use of logic, it’s surprising what you can do with it when you apply it to real life isn’t it? Which as you say, health professionals too often don’t.

    Healthy lifestyle won’t necessarily prevent serious illness either and if we live longer, the horrors of dementia loom larger.

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  4. AKH, I'm always amused by the implication in many US articles that, if such-and-such a disease was eliminated we'd all live for ever.

    Perhaps it's because, being a new nation, they don't have the heritage of the medieval 'memento mori' aspect of religion - 'As I am, so you shall be'.

    That, of course, is easier to accept that the annihilation of personality that comes with dementia - something our society is woefully inadequately equipped to tackle.

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