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更好的数据能否终结全球贫困?

一位杰出的发展经济学家谈到了以数据驱动的方法在解决世界上最棘手的问题方面的优点和局限性。

路透社

一些国家免费发放蚊帐是否会导致疟疾病例增加?抗寄生虫药物在一个国家能提高入学率,而在另一个国家却无效吗?低收入家庭看病所需的预防性医疗费用要低到什么程度?

或许没有完美的方法可以逐个国家地回答这些棘手的问题。但一些顶尖科学家认为,最严谨的答案来自于他们所谓的“随机对照试验”。

埃丝特·迪弗洛被公认为发展经济学领域随机对照试验(RCT)的全球领军人物。作为一种方法论,RCT已在临床医学领域应用超过半个世纪,用于通过设置对照组和治疗组的科学实验来验证或否定药物或医疗程序的效果。利用RCT解决全球贫困问题是近十年才出现的现象,但它已迅速发展,其势头之强劲,堪称经济学、公共政策及其他学科范式转变的典范。

去年,埃丝特·迪弗洛*和她在J-PAL的合作者阿比吉特·班纳吉出版了《贫穷的本质:彻底反思应对全球贫困之道》一书。该书概述了他们通过随机对照试验(RCT)和其他方法所获得的诸多经验,并对关于贫困的“普适答案”和“一概而论的结论”提出了更深刻的质疑。他们建议采用数据驱动的方法,寻求针对性强、切实有效的具体方案,以及成本效益高的方案。埃丝特·迪弗洛被公认为是发展经济学领域随机对照试验的全球领军人物。作为一种方法论,随机对照试验已在临床医学领域应用超过半个世纪,用于通过设置对照组和治疗组的科学实验来验证或否定药物或医疗程序的效果。利用随机对照试验解决全球贫困问题是近十年才出现的现象,但它已迅速发展,成为经济学、公共政策和其他学科领域范式转变的有力例证。

作为一名受过物理学和工程学训练的人,我欣赏并支持迪弗洛运用科学方法对抗贫困的做法。(坦白说,我是“消除贫困创新行动”(Innovations for Poverty Action)的董事会成员,该组织是J-PAL的紧密合作伙伴。)然而,在阅读这本书的过程中,有两点反复浮现在我的脑海中:首先,最好的科学研究既需要理论也需要实验。没有好的理论支撑,数据仅仅是测量结果,而非知识;而强大的理论往往过于笼统。纯粹从实际角度来看,当我们缺乏数据时,理论能够帮助我们更好地理解问题。其次,迪弗洛和班纳吉似乎对他们自己反对给出宏大答案的立场感到不安。本书的大部分章节结尾都包含一些关于公共卫生、教育、小额信贷和创业的概括性论述,这些论述往往缺乏实验的充分支持。尽管如此,他们最后一章的标题“不作一概而论”仍然提出了关于全球贫困人口的五项宽泛论断。

我通过电子邮件向迪弗洛询问了一些关于随机对照试验和她的书的问题……

KT :您认为迄今为止,随机对照试验对国际发展的最大贡献是什么?

ED :首先,我们在一些原本可能还会没完没了争论的问题上取得了很大进展:免费发放蚊帐是否会降低使用率?非零价格是否会降低预防性医疗保健的使用率?其次,我们已经确定了一些有前景的干预措施,并且正在逐步扩大规模,驱虫就是一个典型的例子。[KT:驱虫指的是服用抗寄生虫药物,研究表明,给儿童服用这些药物可以提高入学率。] 第三,我们在某些领域(例如小学教育)积累了足够的知识,开始对问题和解决方案形成更全面的系统性认识。第四,也许也是最重要的一点,政府和组织现在更加认识到在严格观察下进行试验、允许失败的可能性的重要性。我认为从长远来看,这种文化转变可能会成为最大的贡献。

KT :在实际开展、解读或讨论 RCT 时,最大的挑战是什么?或者换句话说,在开展或阅读 RCT 的人群中,您最希望改变的是什么主流做法?

ED :其实我没什么可抱怨的。我认为目前大家都很有创造力,尝试在很多方面突破界限:融入更多理论,将结构模型与实验相结合,将“实验室实验”与随机对照试验相结合,尝试一些非常大胆的做法,比如随机化公务员的工资。

我也很高兴看到 RCT 的应用正在进入政策领域,但我有一个问题:我认为政策制定者愿意利用实验来证明某些做法的合理性,但我们还没有看到的是认真地利用实验来改进政策。

KT :我本科时修读经济学课程,记得当时我就觉得计量经济学很大程度上是为了在随机对照试验(RCT)不切实际的情况下,从数据中提取因果解释。其隐含的假设似乎是,RCT 是理想的选择,但在无法进行 RCT 的情况下,复杂的计量经济学就显得必不可少。这种对经济学方法论的解读是否合理?如果合理,你认为发展经济学为何花了这么长时间才接受 RCT?

ED :我认为,部分原因是我们这个领域可能高估了随机对照试验的难度和成本。迈克尔·克雷默真正的天才之处在于尝试在预算有限的情况下开展随机对照试验。之后,受他的启发,我们中的许多人开始从事类似的工作,并逐渐认识到其他科学领域早已熟知的一点:为学术研究筹集资金是可能的。于是,我们开始筹集更多资金。这两个发现结合起来,彻底改变了整个领域。

KT :您在书中强烈反对任何包罗万象的国际发展理论,这或许可以被解读为对发展复杂性的一种隐性承认。然而,发展经济学中的随机对照试验(RCT)通常是针对特定情境下的人类行为进行的。那么,您的意思是说,人类行为不可能存在包罗万象的理论吗?

ED :理论上当然可以有一些见解,我们在书中也总结​​了一些。但是,并不存在一个能够解释一切的通用框架,或者一个能够解决所有问题的万能方案。

KT :虽然人们对国际发展的目标大致达成共识,但对于最终目标,人们往往有不同的看法。有些人认为每个国家都应该达到一定的经济成就;有些人认为应该是全民医疗保健和教育;还有些人认为应该是社会正义;等等。您心中是否有一个为之努力的最终目标?

ED :我不确定我是否真的对此有自己的看法,或者说我是否应该有看法。我认为目标应该由政治进程来设定,由一个社会在某个阶段认为重要的东西来决定。我可能对生活中什么重要有自己的看法,但我不是哲学家,我不觉得我的职责是告诉人们他们应该认为什么重要。我认为经济学家的职责应该是帮助个人或社会(通过他们的政策制定者)​​在目标设定之后实现这些目标。

***

总之, 《贫穷的本质》是所有关注国际发展人士的必读之作,而且它刚刚发行了平装版。无论你是否相信宏大的理论,都很难否认数据和细致观察的价值。班纳吉和迪弗洛在书中倾注了大量来自个人经验和科学研究的宝贵见解。尽管迪弗洛将她的道德目标让渡给了哲学和公共领域,但她理性而又克制的帮助世界各地贫困社区的热情却跃然纸上。

______

*杜弗洛慷慨地将近期国际发展领域 RCT 浪潮的开端归功于她的同事、哈佛经济学家迈克尔·克雷默,但正是她不懈的努力,以及麻省理工学院阿卜杜勒·拉蒂夫·贾米尔贫困行动实验室 (J-PAL) 同名捐赠者的推动,才使得 RCT 几乎成为主流。

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Noor a.f May 21, 2012
They all necessary. there was another comment disappeared before I made reply. I know there are a lot of things that make harder things. To point first one is trust and it is the backbone of everything. So without going long way of trying tiresome points, tell simplest and reason. Not doing so is lack of trust of the simple ways."we prefer the NGO work to be this way because that way is not best for such...such...such.."You can put it like that way but if you go as far as 1 million pages is lack of trust.If there are certain ways of doing things and you know works best then say the.You didn't cause any problem but some fear and it happens  because of authority.I really don't tolerate violence but when I look the feelings of my actions I feel what innocent Asians would feel like. It was intended the woman who spoke up to be in as cases would be worked. So that she would learn how to respect human feelings and laws but money launderer might saved.Well, I am not complaining anything. I j... [View Full Comment]
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Shirley M May 21, 2012

A couple of things: if you have no food and shelter, you die. If you have no access to health care and hygiene, your life span is severely shortened. If you have no access to education, it's almost impossible to be a part of the solution. So from a purely 'common sense' point of view, I wouldn't have thought the basic necessities of life such as food, shelter, health and education were basics that could be left out of any RTCs. Do we really need to spend time and money figuring out if a 'society' really wants these things? 

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Noor a.f May 19, 2012

Well, it seems there had been misunderstandings about what to be done and how to be done. Woman is repressed  and if she would have known that it is as simple as this she would have owned google seach "N.A" long ago. Well, we teach only what you say and only how you say. Just make next step, it is that I was called today by someone I last knew was in Nairobi and now is very far, Finland.  I recognized her voice before I changed mine because I was in Sale and couldn't ask money nor could I let her know it was me. So I had 3 feeling at one time...So i started to feel shame.
Anyway, our NGO can teach Buddhism, Jews and whatever else you like. Make a progress and I don't mind much about it. All I need is to be on google search for dignity and make something that has value.

Are we together? It is just that simple if you can make and understand people who are left behind. 

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