经济学人28:司法科学 无知即是福

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　　科技

　　Forensic¹ science

　　司法科学

　　Ignorance is bliss²

　　无知即是福

　　Forensic scientists know too much about the cases they investigate

　　法医科学家对他们调查的案子知道得太多

　　AS ALL fans of crime fiction know, DNA³ is the gold standard of forensic science. Or is it? Itiel Dror, a cognitive⁴ psychologist at University College, London, thinks this doctrine⁵ of infallibility needs to be questioned. His problem is not with the technology itself, but with the way it is deployed⁶. For he has gathered evidence that DNA examiners' interpretations⁷ of their results are, at least in complex cases, open to subjectivity⁸ and bias⁹.

　　所有的罪案小说迷都知道，DNA是司法科学的黄金标准。它到底是么？一位伦敦的大学认知心理学专家Itiel Dror认为这个说法的正确性有待考验。他的问题不是针对技术本身而是它进行的方式。因为他已经搜集了证据证明DNA鉴定者对他们结果的解释至少在复杂的案子里易受主观性和偏差的影响。

　　When America's National Academy of Sciences produced a report on the state of forensic science in 2009, it criticised many of the methods then in use. Citing earlier research by Dr Dror, the report's authors stated, for example, that fingerprint¹⁰ examiners' claims of zero error rates were scientifically implausible. DNA, however, was spared their criticism. Now Dr Dror and Greg Hampikian, a forensic biologist at Boise State University in Idaho, have published a study in Science & Justice that suggests all is not shipshape in the domain¹¹ of the double helix either.

　　当美国国家科学院在2009年发表了一片关于司法科学现状的报告时，它批判了很多当时正在应用的鉴定方式。引用这篇报道的作者Dror博士早前做的研究，例如，指纹鉴定者宣称的零误差在科学上是不合理的。然而DNA省去了他们的批判。现在，Dror博士和博伊西的爱达荷州立大学的法医学生物学家Greg Hampikian在"科学与正义"上发表了一篇研究，表明所有的东西都不是井然有序的，在双螺旋线的领域里也不是。

　　Dr Dror's and Dr Hampikian's experiment presented data from a real case to 17 DNA examiners working in an accredited¹² government laboratory in North America. The case involved a gang rape¹³ in the state of Georgia, in which one of the rapists testified against three other suspects in exchange for a lighter¹⁴ sentence, as part of a plea bargain. All three denied involvement, but the two DNA examiners in the original case both found that they could not exclude one of the three from having been involved, based on an analysis of swabs taken from the victim.

　　Dror博士和Dr Hampikian博士的实验提供一个真实案例的数据给17个在一家受认可的北美政府实验室里工作的DNA鉴定员。这起案件涉及到一宗乔治亚州的轮奸案，其中一名强奸犯为了让自己获得轻判做了不利于其它三名嫌疑者的证言，作为认罪辩诉协议的一部分。其他三名嫌疑人全部否认参与强奸，但是根据从受害者处提取的药签分析，原案中有两位DNA鉴定师都发现他们无法排除三名中的其中一名参与了强奸。

　　As is almost always true in forensic-science laboratories, these examiners knew what the case was about. And their findings were crucial to the outcome because in Georgia, as in many other states, a plea bargain cannot be accepted without corroborating¹⁵ evidence. However, of the 17 examiners Dr Dror and Dr Hampikian approached—who, unlike the original two, knew nothing about the context of the crime—only one thought that the same suspect could not be excluded. Twelve others excluded him, and four abstained¹⁶.

　　由于在司法科学实验室里总是什么都是对的，这些鉴定师们知道这个案子到底是怎么回事了。而且他们的手指对于出来的结果是至关重要的，因为在乔治亚，同时也在很多其它州，认罪辩诉如果没有确实的证据是无法被接受的。然而，在Dror博士和Hampikian接触的17个鉴定师中——他们不像开始两位鉴定师那样，对犯罪内容一无所知——只有一位认为一样的嫌疑不能被排除。另外十二位把他排除了，而四位弃权。

　　Though they cannot prove it, Dr Dror and Dr Hampikian suspect the difference in contextual information given to the examiners was the cause of the different results. The original pair may have subliminally¹⁷ interpreted ambiguous information in a way helpful to the prosecution¹⁸, even though they did not consciously realise what they were doing.

　　尽管他们无法证明，Dror博士和Hampikian博士怀疑鉴定师得到的上下文信息的区别是引起这些不同结果的原因。开始的两个人也许已经在下意识里以某种有益于控方的方式破译了模棱两可的信息，即使他们没有清楚地意识到当时他们在做什么。

　　And DNA data are ambiguous more often than is generally realised. Dr Dror thinks that in about 25% of cases, tiny samples or the mixing of material from more than one person can lead to such ambiguity¹⁹. Moreover, such is DNA's reputation that, when faced with claims that the molecule²⁰ puts a defendant²¹ in a place where a crime has been committed, that defendant will often agree to a plea-bargain he might otherwise not have accepted.

　　而且DNA数据往往比普遍了解的要模棱两可。Dror博士认为在大约25%的案子里，小样本或者从不止一人身上取来的混合物质可能导致这样的二义性。此外，DNA的好名声就是这样，当面临宣称用DNA分子证明被告所犯的罪的时候，被告通常会同意认罪辩诉，否则他也许不会接受。

　　This one example does not prove the existence of a systematic²² problem. But it does point to a sloppy²³ approach to science. According to Norah Rudin, a forensic-DNA consultant²⁴ in Mountain View, California, forensic scientists are beginning to accept that cognitive bias exists, but there is still a lot of resistance to the idea, because examiners take the criticism personally and feel they are being accused of doing bad science. According to Dr Rudin, the attitude that cognitive bias can somehow be willed away, by education, training or good intentions, is still pervasive²⁵.

　　这个例子没有证明系统性问题的存在。但是它确实指出了一个科学上草率的方法。根据一位加利福尼亚州芒廷维尤的法庭DNA顾问Norah Rudin，法庭科学家正在开始接受那种认知性偏差的存在，但仍然有很多阻力，因为鉴定师个人会接受批评，觉得自己被谴责说自然科学学得差。根据Rudin博士，认知偏差可以通过某种方式意识性去除的态度是普遍的，比如通过教育、训练或好意的方式。

　　Medical researchers, by contrast, take great care to make drug trials "blind", so that neither the patient nor the administering doctor knows who is receiving the drug being tested, and who is getting a control drug or placebo²⁶. When someone's freedom—and, in an American context, possibly his life, as well—is at stake, it surely behoves forensic-science laboratories to take precautions that are equally strong.

　　相比之下，医学研究者非常注意使药物试验"不透明"，所以病人和用药的医生都不知道接受药物测试的是谁，和控制药物和安慰剂的是谁。在美国环境中，当某人的自由和他的生命也危在旦夕的时候，法医科学实验室应当采取相当的强预防措施。

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