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Statistics may be dull, but they're key to the screening debate

The Jobbing Doctor's VTS students eyes glaze over when it's a session on statistics, but they're vital when considering screening programmes.

The Jobbing Doctor's VTS students eyes glaze over when it's a session on statistics, but they're vital when considering screening programmes.

The Jobbing Doctor also happens to be a Jobbing Educator and for 2 sessions a week I organise and run the local vocational training scheme. It is a wonderful way to keep up to date with clinical and political changes and I am fortunate to have great colleagues who run the scheme with me.

Many of the young doctors are very keen to learn the very clinical subjects and are happy when we run sessions on dermatology, or ophthalmology or other subjects. They are less happy when we cover the softer subjects such as research or ethical diversity. The subject of statistics has a typical reaction, which I believe the Romans called:

‘Oculi Mei fiunt liquidae'

The rough translation of this is ‘my eyes glaze over'.

But it is really quite important, particularly interpreting data.

One of the subjects that is constantly in the public eye is that of screening. This is a more complex subject than many people are aware and the way it is treated in the mainstream media is extremely disappointing. Most people (who do not study the subject) have a simplistic view of the merits of screening, on the basis that it is always a ‘good thing'.

It is not as simple as this and those who look at it this way merely adopt the approach as described by George Orwell in ‘Animal Farm': four legs good, two legs bad.

I teach a session on statistics that are applicable to GPs. The reason I do it, and not my colleagues, is summed up in the phrase

‘In the Kingdom of the blind, the one-eyed man is king'

I might not know much about statistics, but I know more than my teaching colleagues (and hopefully more than the young doctors). So a session always needs to be done on the relationship between a test and the disease: you start to realise the significance of this when looking at, for example, the area of prostate cancer and the prostate-specific antigen blood test (PSA). Generally, we are not coping very well with explaining the limitations of the PSA and the numbers of false positives and false negatives and the issues that they raise.

‘If I have a normal test, that means I don't have prostate cancer, do I doc?' This is specificity. But at best it is only 87% specific, so one in 9 prostate cancers have a normal PSA.

‘If I have an abnormal test, this means I have prostate cancer, don't I doc?' This is sensitivity. It is even worse here, because the current sensitivity of the PSA is 33%. That is, only 1 in 3 men with abnormal PSA have prostate cancer.

Now, your average working-class bloke doesn't read this in his usual reading material, so I patiently explain the risks (horse-racing terms help here). However, the average GP has a pretty slim grasp of this as well, and your average urologist is very much of the ‘four legs good, two legs bad' mentality. I know one who just assumes a PSA of greater than 4 is cancer, it's just that we haven't found it yet.

So I have to teach on these subjects and there are times when I feel that I am like poor old Sisyphus, for ever condemned to push a boulder up the hill, for it to roll straight down to the bottom again.

We subject a lot of people to unnecessary tests and procedures, and those procedures around the prostate are not nice.

So when I reach a certain age, will I have my PSA done? I don't think so.

The Jobbing Doctor Generally, we are not coping very well with explaining the limitations of the PSA and the numbers of false positives and false negatives and the issues that they raise. PSA testing

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