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遇见未知的自己

已有 3299 次阅读 2012-7-12 05:14 |个人分类:心情笔记|系统分类:科研笔记|关键词:学者| support, common, matching

Propensity score matching 是时下经济学评价政策效应的流行方法。或许用生物里的对照实验来解释比较好。假设我们需要了解一种新药的疗效,我们不能同时观察到同一个体接受治疗和没有治疗的结果。所以它的基本思想是在找到未参与者作为对照组,他们接受治疗前特征与实验组应该尽可能的相似,所谓“其他条件一致”。这个特征(common support)的选择,以及相似的标准(matching algorithm)则正是propensity score matching的核心了。这个方法从生物学研究发展到经济学研究政策效应或许都源于个体对自己的思考。


你的面前有两条路,你选择了一条,如何知道选择了另一条与现在的你有多大的差别呢?这个世界再找不到一个同样的你来完成这样的一个实验,所以这对生物学家来说一定是一个难题,因为这无法在实验室完成,对经济学家而言,一定是成本大于收益的。但他们可以找到另一个特质与你及其相似的你,可惜总不能让你的父母生下双胞胎的另一个你来完成这样的一个实验,但无论如何这都是兴师动众的一样活。又或者当人们都好奇到如此,形成了一个市场,让物理学家们来开发这样的一个产品,在另一个星球有另一个你(正物质,反物质?),在交叉口你选择了另一条路,再现在地球上生活的你。让你得以瞥见另一个自己,是欢笑是悲伤,又或者是一样的碌碌无为。这或许应该交给像Robert Frost这样的诗人。

The Road Not Taken

Two roads diverged in a yellow wood,

And sorry I could not travel both

And be one traveler, long I stood

And looked down one as far as I could

To where it bent in the undergrowth;


Then took the other, as just as fair,

And having perhaps the better claim

Because it was grassy and wanted wear,

Though as for that the passing there

Had worn them really about the same,


And both that morning equally lay

In leaves no step had trodden black.

Oh, I marked the first for another day!

Yet knowing how way leads on to way

I doubted if I should ever come back.


I shall be telling this with a sigh

Somewhere ages and ages hence:

Two roads diverged in a wood, and I,

I took the one less traveled by,

And that has made all the difference. 




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