双语新闻:中国“女性缺失”问题与乙肝病毒无关
Economist Scraps Theory On China's 'Missing Women'FOR HER ECONOMICS Ph.D. at Harvard University, Emily Oster found that the ratio of men to women was unusually high in China not only because of a pronounced parental preference for sons, but also because of the effects of the hepatitis B virus.
When her explanation of what is known as the 'missing women' problem came out in 2005, it created a stir and cemented her reputation as a rising star. The authors of 'Freakonomics,' University of Chicago economist Steven Levitt and journalist Stephen Dubner, wrote about her in 'Slate.' Other news media followed. Her paper was published in the prestigious 'Journal of Political Economy,' then edited by Mr. Levitt. She was hired by the University of Chicago, where her reputation for creative research, on topics ranging from television's effect on women's status in India to the links between long-haul trucking and HIV in Africa, has grown.
But Ms. Oster, 28 years old, says newly available data prove that the hepatitis B virus can't explain China's skewed sex ratios. What is more, she contributed to the effort showing that the surprising conclusion that helped make her reputation was wrong.
Mr. Levitt considers that exceptional. 'She did what you would hope good scholars would do but that very few good scholars actually have ever done,' he says.
Ms. Oster's original work built on a hunch from Baruch Blumberg, the Nobel laureate who first identified the hepatitis B virus. Observing high male-female birth ratios among the hepatitis B-infected populations he had studied, he hypothesized that the virus might affect female, but not male, fetuses. China's missing-women problem was usually ascribed to the aborting of girl babies, female infanticide and neglect. But the country has a high frequency of hepatitis B that 'might provide a biological explanation for the apparent loss of female children,' he wrote.
Ms. Oster combed through data and looked at sex ratios in Taiwan and among Native Alaskans following hepatitis B vaccination programs. After crunching the numbers, she determined that, based on 1990 population estimates, the virus might account for 23 million of the 30 million girls who would otherwise be living in China if the country had a naturally balanced gender ratio. (Preference still played a role, she said, and, through the combined effect of China's one-child policy and the availability of ultrasound technology, it appeared to have increased over time.)
It was a controversial finding. China's high male-to-female ratio has led to a surplus of unmarried men and the threat of social and economic instability. If the preponderance of men was largely due to hepatitis B, the Chinese might put more resources toward immunization rather than the more difficult task of altering an ingrained cultural preference for sons.
Other economists working on the missing-women problem cried foul. The World Bank's Monica Das Gupta pointed out that in Chinese families whose first children were daughters, later births tended to be sons. That suggested that families that had girls already were taking measures to ensure they would have a son. Ms. Oster is 'extremely competent,' says Ms. Das Gupta, 'but she has a tendency to want to come up with things that are breathtaking and controversial and new and challenging, which on this occasion led her into trouble.'
Then economists Ming-Jen Lin and Ming-Ching Luoh from National Taiwan University found data from a hepatitis B immunization program Taiwan launched in 1984 that covered three million births. It showed that for children born to women who carried the virus, male-female sex ratios were only slightly elevated, suggesting hepatitis B could explain only 0.9% to 1.8% of China's missing women.
It was still possible that fathers who carried hepatitis B might affect sex ratios, a question unanswered by the Taiwan data. Ms. Oster found a large, continuing study of hepatitis B in rural China. Working with local public-health authorities, she collected data on child gender from 67,511 participants, 15% of whom carried the virus.
Ms. Oster's original paper 'did a good job of using the best evidence available at that time,' says Harvard economist Lawrence Katz, one of her thesis advisers. 'Rather than just coming back and answering critics by reiterating what she said more powerfully she took the initiative to get engaged in new data collection.'
Ms. Oster's new finding: Whether carried by men or women, the virus had no apparent effect on China's birth-sex ratios. She posted a paper, co-written with the Chinese researchers, 'Hepatitis B Does Not Explain Male-Biased Sex Ratios in China,' on her Web site last month.
'I'd be lying if I told you it wouldn't be great if I was right all the time,' Ms. Oster says. 'If you work like this, especially if it's something that people care about, and you get to collect some more data that is maybe going to be even more informative than what you had before, it's your responsibility to do that. This is the way science works.'
中国“女性缺失”问题与乙肝病毒无关
在哈佛大学(Harvard University)攻读经济学博士学位时，艾米莉.奥斯特(Emily Oster)通过研究发现，中国男女比例明显失衡的背后不仅有父母重男轻女的观念作祟，同时也有乙肝病毒的影响。
2005年奥斯特发表论文，对所谓的“女性缺失”(missing women)问题提出了自己的解释，这不仅引起了一场轰动，也巩固了她学术新星的声誉。《魔鬼经济学》(Freakonomics)的两位作者──芝加哥大学(University of Chicago)经济学家史蒂芬.列维特(Steven Levitt)和记者史蒂芬.杜伯纳(Stephen J. Dubner)在Slate网站上撰文对她进行了介绍。随后其他媒体也相继报导。她的这篇论文发表在大名鼎鼎的《政治经济学期刊》(The Journal of Political Economy)上，由列维特进行编辑。奥斯特后来受聘于芝加哥大学，她在那里从事了一系列创新性研究，研究课题从电视对印度妇女地位的影响到非洲长途卡车运输与艾滋病病毒(HIV)的关系，学术声望也不断上升。
然而，28岁的奥斯特现在表示，新的数据证明乙肝病毒无法解释中国的男女比例失衡问题。而且，在驳倒这个曾经使她声名鹊起的惊人结论的研究中，她自己也付出了努力。
列维特认为，奥斯特的这一举动不同寻常。他表示，这是一名杰出学者应该具备的品质，但却很少有人能真正做到。
奥斯特最初的研究建立在巴鲁克.布隆伯格(Baruch Blumberg)的研究基础之上，后者最早发现了乙肝病毒并因此获得了诺贝尔奖。布隆伯格发现，他所研究的乙肝病毒携带者中，生男孩的比例明显高于女孩。他由此提出假说，认为病毒可能会感染女性胎儿，但不会影响男性胎儿。中国的“女性缺失”问题通常被归咎于选择性堕胎、女婴遭扼杀和遗弃等原因。但布隆伯格写道，中国的乙肝病毒感染比例很高，这或许为该国明显的男女出生率失衡问题提供了一个生物学上的解释。
奥斯特对数据进行了分析梳理，并研究了台湾与阿拉斯加居民在接种乙肝疫苗后的男女出生率情况。她在对数据进行分析之后判定，按照1990年的人口估计数据，中国缺失的3,000万女孩（根据正常均衡的出生率推算）中，可能有2,300万都是乙肝惹的祸。（她也承认，重男轻女的观念仍然是一个重要的原因；而且，在中国计划生育政策以及B超技术普及的双重推动下，这一因素的比重似乎在逐渐上升。）
一石激起千层浪，她的观点当时在学术界引起诸多争议。中国男女比例失衡的问题不仅造就了大量的光棍，也危害到了社会和经济稳定。如果男性过多的问题主要是由乙肝引起的话，那么中国就可以在普及乙肝疫苗接种，而不是纠正根深蒂固的重男轻女观念方面投入更多的资源。相比之下，转变观念这个任务要艰巨的多。
其他研究“女性缺失”问题的经济学家则对此持有异议。世界银行(World Bank)的莫妮卡.达斯.古普塔(Monica Das Gupta)指出，头胎生女孩的中国家庭，随后生育的往往是男孩。这表明，已生女孩的家庭会想办法确保生个男孩。达斯.古普塔认为，奥斯特的确能力出众，但她总想标新立异、独树一帜，这使她在这项研究中陷入了误区。
国立台湾大学的经济学家林明仁和骆明庆对台湾1984年推行的乙肝疫苗接种项目数据进行了研究，该项目覆盖了300万名新生儿。研究发现，在携带乙肝病毒的母亲中，所生育的男女孩比率只是略有上升。这表明，中国的女性缺失中，可能只有0.9%-1.8%是由乙肝病毒引起的。
但是，也有可能是携带乙肝病毒的父亲影响了性别比率，这个问题没有在上述台湾数据中得到解答。奥斯特得知对中国农村地区的乙肝问题正在进行一项广泛的持续性研究。她与当地医疗卫生部门合作，收集了67,511名研究对象的生育性别数据，其中有15%的研究对象是乙肝病毒携带者。
哈佛大学经济学家劳伦斯.卡兹(Lawrence Katz)说，奥斯特最初的那篇论文使用了当时能找到的最好资料来论证她的观点，这方面她做的不错。卡兹是奥斯特当时的论文指导老师之一。他表示，奥斯特并没有原地踏步，固守原有观点来应对学术界的质疑，而是投身到新数据的收集之中。
现在奥斯特提出了她的新观点：父母是否携带乙肝病毒对中国新生儿性别比例并没有明显的影响。上个月她在自己的网站上发表了一篇与中国研究人员合著的论文《乙肝病毒无法解释中国男女比例失衡问题》(Hepatitis B Does Not Explain Male-Biased Sex Ratios in China)。
奥斯特说，“如果说我不想自己的观点始终无懈可击的话，那么我就是在撒谎。但如果你从事研究工作，尤其是研究那些人们关注的问题的话，当你需要著手收集更多的数据──这些数据可能甚至比已有的数据提供的信息还要多，那么你就有责任去做。这是科学的进步之道。”
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