回复 7# szwuxl
今日阅读了一篇发表于《独立报》的短文,该文从学术的角度,批评了世界卫生组织一研究小组在《柳叶刀》上发表的一篇学术论文。这篇短文的作者Nigel Hawkes,是Straight Statistics的头,自然是统计学领域顶尖权威人物。而世界卫生组织是世界医学顶尖权威组织,《柳叶刀》是生物医学领域顶尖权威期刊,《独立报》又是新闻界知名报纸。真有趣。兴头上,将这篇短文一气翻译下来,并找到它所批评的《柳叶刀》上那篇学术论文的链接,一并附于此。
这两篇文章,从学术的角度,谁是谁非,只有用循证医学研究方法中的重要的严格评论(或是译为严格批评?)的方法,把《柳叶刀》上的那篇文章仔细分析后,才能判断。 从这也可以看出,一篇医学论文,不管它的作者是谁,不管它发表在那里,都必须用严格评论的方法来解读。
一个对于剖腹产的偏倚的坏例子 ―― 数字的背后
作者:Nigel Hawkes
世界卫生组织不赞成过多医疗干预的分娩,这或许是有道理的。太多的剖腹产手术,是在没有正当理由的情况下实施的。
不过,这并不能靠发表没有说服力的证据 ―― 如最近所刊登于《柳叶刀》上的一篇文章那样,来改进这种状况。那篇(发表于《柳叶刀》上的)文章的23个作者总结道:对于没有医学指征(表明需要行剖腹产)而选择剖腹产的产妇,死亡率或并发症的可能性比正常分娩的产妇高2.7倍。
这足够使人胆颤心惊到望而生畏的地步;我猜想这也正是作者们的意图。不幸的是,他们的结论并不是从他们所摆出来的证据中推出来的。这个世界卫生组织全球孕产妇围产期健康研究调查组,调查了亚洲107950份分娩病历。其中,1515个是产前没有医学指征而选择剖腹产,而且几乎全部发生在中国。
那么,这其中多少产妇死于剖腹产?无。多少发生了并发症?8例;其中5例需重症监护,3例需要输血。然而这种风险的发生率,在完成自然分娩的产妇中,却显著高于剖腹产产妇:即千分之一的死亡率,需输血者高5倍,以及需重症监护者高两倍。
因此,如果将死亡率和并发症来计算一个‘围产期死亡率和并发症指标’,那么剖腹产产妇的这些风险,比正常分娩产妇低60%。
那么,究竟这个调查研究组是如何得出剖腹产妇的风险高于自然分娩产妇的2.7倍这个结论来的呢?低于60%,与高于270%,是一个巨大的差别,只是,统计学上的人为操纵,是一项强有力的工具。
这个调查研究组通过(从统计学上)矫正一系列的风险因素,从而达到了他们的转换。要是(结果显示)剖腹产妇组是一个低风险组,那么很可能,这样的矫正可以缩小甚至消除这种(剖腹产组与自然分娩组之间风险的)差别。这种情况下,这(纳入统计学)矫正(的风险因素),包括年龄、受教育情况、过去病史、高血压等等。
要算出那些风险因素必须多低才能对原始数据做如此大的矫正,是很容易的事。只要使剖腹产妇组的基础风险仅为自然分娩产妇组的1/7,就行得通了。这真是难以置信。
尽管在该文章里,作者们对这些数据的显著的转换,也有过注释,但他们却仍说:“这个调查最重要的发现是:增高的围产期死亡率和严重的并发症;这是对无医学指征而行剖腹产的产妇综合分析的结果。”
难道这23个作者中没有任何一个人想一想这项调查研究之奇怪的结论?难道没有一个人检查一下那些表格中错误百出的计算?《柳叶刀》是一个杰出的杂志,难道它的审阅者们都睡着了么?
行家们将医学作者们拼命去做出来的‘正确答案’,称做“白帽子偏倚”,―― 旧式的西方英雄们总会赢得一顶白帽子。这里就是一个典型的例子。政策说剖腹产是不好的,那么证据最好就能够证明它是不好的。
至于那些婴儿,又如何呢?那些没有医学指征而选择剖腹产所剖出的婴儿,他们的死亡率和并发症低于自然分娩儿的7倍(根据原始数据),或少于自然分娩儿的二分之一(根据矫正数据,如果你相信那些矫正数据的话)。可以理解地,那些作者们不愿在这个方面(即针对这些关于婴儿的数据)多提。
本人注:“白帽子偏倚”,是一种统计学上的偏倚,即导致“信息曲扭和失真、却可能被认可为公正结果”这种现象的偏倚。
附一:原文(链接http://www.independent.co.uk/lif ... areans-1883667.html)
A bad case of bias against caesareans – behind the numbers
The World Health Organisation disapproves of over-medicalising birth, and it's probably right. Too many Caesareans are done for no good reason.
But it isn't going to advance its case by publishing evidence as unconvincing as that in a recent Lancet paper. The 23 authors concluded that a mother who opts for a Caesarean without a good medical reason is 2.7 times as likely to suffer death or complications as a mother who completes a normal birth.
That's enough to put the fear of God into the "too posh to push" brigade, which I suspect was the authors' intention. Unfortunately, the conclusion is in no way supported by the evidence presented. The team, from the WHO's global survey on maternal and perinatal health research group, looked at medical records from 107,950 births in Asia. Of these, just 1,515 were Caesareans chosen in advance of birth with no medical indication to justify them. Almost all of them were in China.
So how many women died? None. How many suffered complications? Eight: five needed treatment in an intensive care unit (ICU), and three needed a blood transfusion. The risks for women who completed a normal birth were significantly higher. One in a thousand died, five times as many required a blood transfusion, and twice as many were admitted to an ICU.
Overall, if deaths and complications are added up to make a "Maternal mortality and morbidity index", risks to mothers in the Caesarean group were 60 per cent lower than in the normal birth group.
So how, from this, does the team conclude that risks to mothers who have Caesareans are actually 2.7 times greater? There's a hefty difference between 60 per cent smaller and 270 per cent greater, but statistical manipulation is a powerful tool.
The team achieves this transformation by correcting for a range of risk factors. If the Caesarean mothers were an especially low-risk group, then it is possible that such a correction could narrow the gap or even eliminate it. The adjustments in this case included such things as age, education, previous medical disorders, high blood pressure, and so on.
It's easy enough to work out how much lower the risks must have been to make such a huge correction to the raw data. The women who had Caesareans must have had only one seventh as much baseline risk as those who had a natural birth in order to make it work – and that's highly implausible.
Nowhere in this paper does the team comment on the remarkable transformation of the figures. But they do say: "The most important finding of the survey is the increased risk of maternal mortality and severe morbidity which was analysed as a composite outcome in women who undergo Caesarean section with no medical indication."
Did none of the 23 think this an odd conclusion to have reached? Did no one check the arithmetic in the tables, which are full of errors? The Lancet is a distinguished journal – were its referees asleep?
Connoisseurs of the bending over backwards that medical authors do to get the "right" answer call it White Hat bias, after old-style Westerns where the hero always wore a white hat. This is a classic example. Policy says Caesareans are bad, so the evidence had better prove it.
And what about the babies? Those born by elective Caesarean without medical indications were seven times less likely to suffer death or complications (raw data) or less than half as likely if you believe the corrected data. Understandably, the authors don't make much of this.
Nigel Hawkes is director of Straight Statistics
附二:《柳叶刀》上世界卫生组织的相关论文链接http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(09)61870-5/fulltext |