Today I read in the Daily Mail...no folks I don't buy the rag....an interview with David Cameron.
The Mail's headline is " Cameron: Cut the abortion limit to 21 weeks" The reason he gives for supporting this is:
"I would like to see a reduction in the current limit, as it is clear that, due to medical advancement, many babies are surviving at 24 weeks."
And the Mail with it's usual selective use of statistics on the issue of abortion continues by asserting
"Research at one of Britain's top neonatal units revealed the survival rate of babies born very prematurely has doubled in the past 20 years."
I suspect the research, both Cameron and the Mail are quoting, is from John Wyatt. He is the Professor of Neonatal Paediatrics at University College, London, and a member of the Christian Medical Fellowship (CMF).
He gave evidence before the House of Commons Committee on Science and Technology last Autumn. Professor Wyatt failed to tell the Committee that he was a member of the CMF with an established position, on abortion, similar to that of the Daily Mail,.
Wyatt's research does indeed show that survival in births below the present limit if 24 weeks has doubled. But when you examine the data from the Epicure study, the picture is very different indeed. That study shows an increase in survival at 24 weeks but virtually none with births between 22 and 23 weeks. The idea punted by Cameron.
The next statistical analysis has been done brilliantly by Bad Science's Dr. Ben Goldacre. You can read his piece in full here. What Wyatt does is play around with figures.
Over to Dr. Ben.
For the next bit, you need to understand one simple piece of primary school maths, which is central to medical statistics. In the sum 3/20, 3 is the numerator and 20 is the denominator: 15% survive; 3 out of 20. For Epicure, the numerator is survival to discharge from hospital, and the denominator is all births where there is a sign of life, carefully defined: 3 out of 20.
I suspect you can see where this is going?
Back to Goldacre.
There are two ways you could get a higher survival percentage. One would be a genuine increase in the number of babies surviving, an increase in the numerator: 8 out of 20 live births survive, 40%. But you could also see an increase in the survival percentage by changing the denominator. Let's say, instead of counting as your denominator "all births where there is a sign of life in the delivery room" you counted "all babies admitted to neonatal intensive care". Now that's a different kettle of fish altogether. To be admitted to neonatal ICU, the doctors have to think you've got a chance. Often you have to be transferred from another hospital, in an ambulance, and for that you really do have to be more well. Therefore, if your denominator is "neonatal ICU admissions", your survival rates will be higher, but you are not comparing like with like. That may partly explain Prof Wyatt's figure for a very high survival rate in 23-week babies. But it's not clear.
He now examines the evidence Wyatt gave to the House of Commons Committee.
First in his written evidence he said that the data was from a "prospectively defined" study (where they say in advance what they plan to collect). Then he was asked in the committee, when giving his oral evidence: "What was the denominator for that? Was that ... 42% survival at 23 weeks of all babies showing signs of life in the delivery room, or was it a proportion of those admitted to neonatal intensive care directly or by transfer?" Prof Wyatt replied: "The denominator was all babies born alive in the labour ward in the hospital at UCL [University College London]." This, as later became clear, turned out not to be true. Then he was asked to send the reference for the claim. He did so. It was merely an abstract for an academic conference presentation three years ago. It did not contain the figures he was quoting. He then says he has done the raw figures on a spreadsheet, especially for the committee, bespoke, if you will, and sent them in. They are entered into the record as a memo, on October 18. They show new, different, although broadly comparable figures: 50% survive at 22 weeks, then down to 46% at 23 weeks, then up to 82% at 24 weeks, then down again to 77% at 25 weeks. (That bouncing around is because the raw numbers are so small that there is a lot of random noise).
Are you still with this? When asked about the denominator
Prof Wyatt is clear: "I have provided the numbers and percentage of infants born alive at University College London Hospitals who survived to one year of age." The committee asked for clarification of this. Finally, October 23, another memo arrived, from Prof Wyatt, entered into the record, for all to see. For the widely quoted 42% survival rate at 23 weeks, Prof Wyatt admitted that the denominator was all babies admitted to the neonatal intensive care unit. But in his new special analysis, giving this new "46% survive at 23 weeks" figure, the figures in the previous paragraph, he claimed, the denominator was "all live births". Has he undone a prospectively designed study, and retrospectively re-designed it? Or is this now a completely different source of data to the original reference?
Like drawing teeth isn't it?
Goldacre's devastating conclusion follows
But science is about clarity and transparency, especially for public policy. You need to be very clear on things like: what do you define as a "live birth", how do you decide on what gestational age was, and so on. Even if this data stands up eventually, right now it is non-peer reviewed, non-published, utterly chaotic, personal communication of data, from 1996 to 2000, with no clear source, and with no information about how it was collected or analysed. That would be fine if it hadn't suddenly become central to the debate on abortion.
Cameron and his advisers have fallen headlong into the Daily Mail's statistical trap, Why on earth they didn't listen to the British Medical Association and the Royal College of Obstetricians and Gynaecologists who have said they do not believe there is a case for changing the time limits for abortion.