Planning a Study · 规划一项研究
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| observational study/ɒbzəˈveɪʃənl ˈstʌdi/ | 观察性研究 | guān chá xìng yán jiū |
| experiment/ekˈsperɪmənt/ | 实验 | shí yàn |
| cause-and-effect/kɔːz ænd ɪˈfekt/ | 因果关系 | yīn guǒ guān xì |
| sample/ˈsæmpl/ | 样本 | yàng běn |
| confounding variable/kənˈfaʊndɪŋ ˈveərɪəbl/ | 混杂变量 | hùn zá biàn liàng |
Watching vs. doing
- Two ways to gather data: an observational study 观察性研究 or an experiment 实验.
- In an observational study you watch and measure — you don't change anything.
- In an experiment you impose a treatment and see what happens.
- The difference decides whether you can claim cause-and-effect 因果关系.
观察还是干预
- 收集数据有两种方式：观察性研究或实验。
- 在观察性研究中，你只是观察并测量——不改变任何东西。
- 在实验中，你施加一种处理，再看会发生什么。
- 这个区别决定了你能否宣称因果关系。
Population and sample
- The population is the whole group you want to learn about.
- The sample 样本 is the smaller part you actually study.
- You measure the sample, then hope to generalize back to the population.
- Good design keeps the sample a fair stand-in for the population.
总体与样本
- 总体是你想了解的整个群体。
- 样本是你实际研究的那一小部分。
- 你测量样本，然后希望能推广回总体。
- 好的设计让样本成为总体的公平替身。
Only experiments prove cause
- To show $X$ causes $Y$, you must actively assign $X$ and hold other things comparable.
- That's what an experiment does — and why only it can establish cause-and-effect.
- An observational study can reveal an association but never prove the cause.
- If you didn't control who got the treatment, you can't rule out other explanations.
只有实验能证明因果
- 要证明 $X$ 导致 $Y$，你必须主动分配 $X$，并让其他因素保持可比。
- 这正是实验所做的——也是只有它能确立因果的原因。
- 观察性研究能揭示关联，但永远无法证明原因。
- 如果你没有控制谁接受处理，就无法排除其他解释。
The confounding trap
- In an observational study, a confounding variable 混杂变量 can create a misleading link.
- A confounder is tied to both the explanatory and the response variable.
- It makes two things look causally linked when a third factor drives both.
- This is exactly why "observed association" ≠ "cause."
混杂陷阱
- 在观察性研究中，一个混杂变量能制造出误导性的联系。
- 混杂因素同时与解释变量和响应变量相关联。
- 它让两件事看起来有因果联系，而实际上是第三个因素在驱动两者。
- 这正是“观察到的关联”≠“因果”的原因。
The single most important distinction in Unit 3: only a well-designed experiment (with random assignment) can establish cause-and-effect. An observational study — however large or careful — can show association but is always open to a confounding variable, so it cannot prove that the explanatory variable caused the response.
第 3 单元中最重要的区分：只有设计良好的实验（带随机分配）才能确立因果关系。**观察性研究——无论多大或多仔细——只能显示关联，且始终对混杂变量**敞开大门，因此无法证明解释变量导致了响应。
Do vitamins improve health?
- Observational: compare people who choose to take vitamins vs. those who don't. Vitamin-takers may also exercise more — a confounder. No causal claim.
- Experiment: randomly assign people to vitamins or placebo. Random assignment balances exercise across groups → a causal conclusion is possible.
维生素能改善健康吗？
- 观察性：比较选择服用维生素的人和不服用的人。服用者也许还更常锻炼——一个混杂因素。无法下因果结论。
- **实验：**随机分配人们服用维生素或安慰剂。随机分配把锻炼在各组间平衡开 → 才可能得出因果结论。
An observational study watches without intervening; an experiment imposes a treatment. You study a sample to learn about a population. Only an experiment with random assignment can establish cause-and-effect — an observational study is always vulnerable to a confounding variable.
观察性研究只观察而不干预；实验施加一种处理。你研究一个样本来了解一个总体。只有带随机分配的实验才能确立因果——观察性研究始终易受混杂变量影响。
A sample drawn from a population · 从总体中抽取的样本
The sample is a slice we study to learn about the whole. · 样本是我们研究的一小块，用来了解整体。
Which type of study can establish a cause-and-effect relationship? · 哪种研究能确立因果关系？
Only random assignment in an experiment supports causation. · 只有实验中的随机分配才支持因果。
In an observational study, the researcher imposes a treatment on the subjects. · 在观察性研究中，研究者对受试者施加一种处理。
Observational = watch and measure without intervening; experiments impose treatments. · 观察性 = 只观察测量、不干预；实验才施加处理。
The whole group you want to learn about is the ___. · 你想了解的整个群体是 ___（填英文一词）。
You study a sample to learn about the population. · 你研究样本以了解总体。
Vitamin-takers also exercise more, muddying a study of vitamins and health. Exercise is a... · 服用维生素者也更常锻炼，搅乱了对维生素与健康的研究。锻炼是一个……
It's tied to both taking vitamins and to health — a confounder. · 它同时与服维生素和健康相关——一个混杂因素。
Which are true of experiments (vs. observational studies)? · 关于实验（相对于观察性研究），哪些是正确的？
Experiments impose treatments and, with randomization, support causation. · 实验施加处理，并通过随机化支持因果。