Thursday, 26 January 2017

An interesting medical scam

When I was writing the chapter about the pink alternative medicine clinic, I found myself challenged to come up with something so bizarre that it would be obvious it was a satire. Just so, I later discovered that bananas occasionally emit positrons. This means that the wobbly bananas I described are occasionally sending out electrons that are going backwards in time.

No doubt sooner or later someone in the alternative medicine world will conclude that sufficient exposure to wobbly bananas, preferably while lying naked on a couch, can make you younger. Of course you'd have to be properly quantumly entangled with the bananas.

However there are some forms of medical wackyology that are more cleverly dressed in the outer garments of science and can fool even quite intelligent people. I here present one such piece of tomfoolery for your education.

It works like this: the practitioner promises to improve the patient's health by re-balancing them. To do this he or she orders a very large number of blood tests. Then, if there are any blood tests that are abnormal the practitioner will offer to rectify this by prescribing some supplement or other.

Sounds reasonable, doesn't it? After all, if someone feels tired and their doctor finds out that they have a deficiency of (say) iron, they can fix it by prescribing iron tablets.

However, medicine is generally a bit more complicated than that. If someone is genuinely iron-deficient it is important to ask why, and to look for the cause. In this context, merely 're-balancing' could be dangerously negligent.

The real basis of the scam is actually mathematical. Consider a field full of women of the same age. Line them up according to height. Most of them will be somewhere around the average, but there will be a few really short ones and a few really tall ones. Even if we remove the ones who are tall or short because of some medical abnormality, there will still be a variation. Thus, healthy people can be tall or short, and a few will be extra tall or extra short without there being anything wrong with them.

(Image taken from this web site)

When the laboratory measures something in someone's blood, most of the time the result will be somewhere in the middle of the range, but some results will be outliers. This will happen fairly often even in perfectly healthy people. There is no absolute cut-off where something suddenly becomes abnormal. The laboratory somewhat arbitrarily defines the range as the middle 95% of values. This should not be referred to as 'the normal range,' rather, it is properly referred to as 'the laboratory reference range.'

It's the same thing with height. If a child is in the bottom 10% for height, you don't think much about it, especially if their parents are short too. If they are in the bottom 2% for height, you start wondering if there is a problem, and you look at the parents' heights and at the previous measurements of growth to see if there is a pattern suggesting disease or not.

In the same way, if a laboratory value is outside the laboratory reference range, you ask yourself if there is a pattern to it or not (such as, all the liver tests are out and the patient drinks too much, or, only one of them is out and the patient is a perfectly healthy teetotaller).

So now we come to the essence of the scam. One or two values being 'out' may or may not indicate a disease process. What is the probability that at least one value will be out in a perfectly healthy person?

Consider first the simpler case of tossing a coin. What is the probability that it will be heads? Fairly obviously 1 in 2, or half, or as normally expressed, a probability of 0.5.

What is the probability that it will be heads twice in two tosses? The answer is the probability that it will be heads the first time multiplied by the probability that it will be heads the second time: 0.5 x 0.5 = 0.25 (a quarter). Three times in three tosses? 0.5 x 0.5 x 0.5 = 0.125 (an eighth) - and so on. What is the probability that in three tosses of a coin at least one will be tails? 1 - 0.125 = 0.875 (seven-eighths).

To do our calculation we use the same process. The probability of a test being within the laboratory reference range is 0.95 (19 times out of 20). The probability of  two tests being within the reference range is 0.95 x 0.95 = 0.9025 (nearer 18 times out of 20). We multiply the probability together with itself the number of times there are tests. If there are 20 tests that is 0.95^20=0.36. This is the probability that all the tests will be 'normal' - just over a third. To get the probability of at least one test being 'out' we subtract this number from 1. So if we do 20 tests on a healthy person, the probability that at least one will be out of range is almost two-thirds (0.64).

For thirty tests the probability of at least one test being 'out' is 0.78, or more than three-quarters. So in such a case on average three out of four healthy people will be convinced they need 're-balancing' and will no doubt purchase whatever is recommended to do the re-balancing, plus of course the consultation fee. Of course this is unlikely to make any difference to anything so they'll be back for more until they decide to save their money and get on with the rest of their lives.

I'm not a cynic, I am simply reporting what I see. As the saying goes, 'you do the math.'

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