MIGUEL HERNAN: Cigarette smoking is one of the most important global health problems.
The World Health Organization estimates that
tabacco kills about six million people each year.
Cigarette smoking has a causal effect on many cancers
如癌症 心脏病 中风 呼吸道疾病等等
and heart disease, stroke, respiratory diseases, you name it.
但这些大家都知道 对吧?
But everybody knows this, right?
然而几十年来 香烟广告上都是健康而强壮的人在抽烟
And yet for decades cigarette ads showed tough, healthy men smoking.
But reality is something hard to argue against.
At least four Marlboro men died of smoking related diseases.
And some well-known Hollywood actors also advertised cigarettes.
有一位死于癌症 另一位死于失智症
One died of cancer, the other of dementia,
which begs the question: does smoking have a causal effect
on the risk of dementia.
There are biological reasons why smoking
increase the risk of at least some forms of dementia.
但是 我们绝不会对吸烟进行随机实验
However, we will never have a randomized trial of cigarette smoking.
幸运的是 这种不道德的实验是不被允许的
Fortinately, such unethical trial is not allowed.
That means that we’ll have to rely on observational data only.
事实上 一些关于抽烟和失智症的前瞻性观测研究
In fact, several observational prospective studies of smoking and dementia
have been conducted since the 1990s.
但是 这些观测性研究所得出的结果却非常迥异
However, the findings of these observational studies vary dramatically.
Some studies found a higher risk of dementia in smokers than in nonsmokers.
Other studies found the opposite.
Can we interpret any of these associations
as the effect of smoking on dementia?
如果真是这样 那答案又是什么呢?
And if so, what’s the answer?
Does smoking cause or prevent dementia?
而且最重要的是 为什么不同的研究获得的结果不同?
And most importantly, why do results differ across studies?
One possibility is uncontrolled confounding in some of the studies,
例如 酒精
for example, by alcohol.
People who become cigarette smokers also tend to drink more alcohol.
If alcohol increases the risk of dementia,
then we would expect to find an association between smoking and dementia,
even if smoking had no effect on dementia.
But it looks like many observational studies of smoking
and dementia did adjust for the most important confounders.
那么 为什么在某些研究中 烟民患失智症的风险更高
Then why did the smokers have a higher risk of dementia in some studies
and a lower risk of dementia in other studies?
Let me give you a hint.
Perhaps it has to do with the selection of individuals
in each of these studies.
We will return to this problem at the end of this lesson.
到那时 你就能够解释这是怎么回事儿了
And by then you will be able to explain what’s going on here.


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