布拉德利的幽灵

Paul Graham 2004-11-01

布拉德利的幽灵

2004年11月

很多人现在在写为什么克里失败了。这里我想探讨一个更具体的问题:为什么出口民调如此错误?

在俄亥俄州,克里最终以49-51失败,出口民调却给了他52-48的胜利。这不仅仅是随机错误。在每个摇摆州,他们都高估了克里的选票。在佛罗里达州,布什最终以52-47获胜,出口民调预测势均力敌。

(这些不是早期数字。它们来自东部时间大约午夜,俄亥俄州和佛罗里达州投票结束后很久。然而到第二天下午,网上的出口民调数字与实际结果相符。我能想象这种情况发生的唯一方式是,负责出口民调的人在看到实际结果后篡改了数据。但那是另一个问题。)

发生了什么?问题的根源可能是布拉德利效应的一种变体。这个术语是在汤姆·布拉德利这位黑人洛杉矶市长尽管在民调中领先优势却在加州州长选举中失败后发明的。显然,选民害怕说他们计划投票反对他,以免他们的动机被(也许正确地)怀疑。

今年出口民调可能发生了类似情况。理论上,出口民调应该非常准确。你不是在问人们会做什么。你在问他们刚刚做了什么。

问这个怎么会出错?因为有些人不回应。为了获得真正随机的样本,民意调查员会说,询问离开投票场的每第20个人他们投票给了谁。但不是每个人都想回答。民意调查员不能简单地忽略那些不愿回答的人,否则他们的样本就不再随机了。所以他们所做的,显然是记下这个人的年龄、种族和性别,并据此猜测他们投票给了谁。

只要人们投票给谁和他们是否愿意谈论之间没有相关性,这就有效。但今年可能有相关性。可能是相当多投票给布什的人不想这么说。

为什么不?因为美国人的保守程度超过他们愿意承认的程度。这个国家精英的价值观,至少目前,是NPR价值观。普通人,正如我认为共和党和民主党都会同意的,在社会问题上更保守。虽然有些人公开炫耀他们不分享精英意见的事实,但其他人对此感到有点紧张,好像他们有不良餐桌礼仪。

例如,根据当前的NPR价值观,你不能说任何可能被视为对同性恋者贬损的话。这样做就是”恐同”。然而,大量美国人深信宗教,而圣经在同性恋问题上相当明确。他们该怎么办?我认为许多人做的是保留他们的意见,但只保留在自己心里。

他们知道自己相信什么,但他们也知道他们应该相信什么。所以当一个陌生人(例如,民意调查员)询问他们对同性婚姻等事情的意见时,他们不会总是说出他们真正想的。

当精英的价值观是自由派时,民意调查倾向于低估普通选民的保守程度。这似乎是解释为什么今年出口民调如此错误的主要理论。NPR价值观说应该投票给克里。所以所有投票给克里的人都觉得这样做是道德的,并急于告诉民意调查员他们这样做了。没有人投票给克里是作为一种安静的反抗行为。

支持女性总统

日语翻译

如果你喜欢这个,你可能也喜欢黑客与画家。

Bradley’s Ghost

November 2004

A lot of people are writing now about why Kerry lost. Here I want to examine a more specific question: why were the exit polls so wrong?

In Ohio, which Kerry ultimately lost 49-51, exit polls gave him a 52-48 victory. And this wasn’t just random error. In every swing state they overestimated the Kerry vote. In Florida, which Bush ultimately won 52-47, exit polls predicted a dead heat.

(These are not early numbers. They’re from about midnight eastern time, long after polls closed in Ohio and Florida. And yet by the next afternoon the exit poll numbers online corresponded to the returns. The only way I can imagine this happening is if those in charge of the exit polls cooked the books after seeing the actual returns. But that’s another issue.)

What happened? The source of the problem may be a variant of the Bradley Effect. This term was invented after Tom Bradley, the black mayor of Los Angeles, lost an election for governor of California despite a comfortable lead in the polls. Apparently voters were afraid to say they planned to vote against him, lest their motives be (perhaps correctly) suspected.It seems likely that something similar happened in exit polls this year. In theory, exit polls ought to be very accurate. You’re not asking people what they would do. You’re asking what they just did.

How can you get errors asking that? Because some people don’t respond. To get a truly random sample, pollsters ask, say, every 20th person leaving the polling place who they voted for. But not everyone wants to answer. And the pollsters can’t simply ignore those who won’t, or their sample isn’t random anymore. So what they do, apparently, is note down the age and race and sex of the person, and guess from that who they voted for.This works so long as there is no correlation between who people vote for and whether they’re willing to talk about it. But this year there may have been. It may be that a significant number of those who voted for Bush didn’t want to say so.

Why not? Because people in the US are more conservative than they’re willing to admit. The values of the elite in this country, at least at the moment, are NPR values. The average person, as I think both Republicans and Democrats would agree, is more socially conservative. But while some openly flaunt the fact that they don’t share the opinions of the elite, others feel a little nervous about it, as if they had bad table manners.For example, according to current NPR values, you can’t say anything that might be perceived as disparaging towards homosexuals. To do so is “homophobic.” And yet a large number of Americans are deeply religious, and the Bible is quite explicit on the subject of homosexuality. What are they to do? I think what many do is keep their opinions, but keep them to themselves.

They know what they believe, but they also know what they’re supposed to believe. And so when a stranger (for example, a pollster) asks them their opinion about something like gay marriage, they will not always say what they really think.When the values of the elite are liberal, polls will tend to underestimate the conservativeness of ordinary voters. This seems to me the leading theory to explain why the exit polls were so far off this year. NPR values said one ought to vote for Kerry. So all the people who voted for Kerry felt virtuous for doing so, and were eager to tell pollsters they had. No one who voted for Kerry did it as an act of quiet defiance.


Support for a Woman President

Japanese Translation

If you liked this, you may also like Hackers & Painters.