| English | 의미 |
|---|---|
| observational study/ɒbzəˈveɪʃənl ˈstʌdi/ | 관찰 연구 |
| experiment/ekˈsperɪmənt/ | 실험 |
| cause-and-effect/kɔːz ænd ɪˈfekt/ | 인과 관계 |
| sample/ˈsæmpl/ | 표본 |
| confounding variable/kənˈfaʊndɪŋ ˈveərɪəbl/ | 혼잡 변수 |
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.
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.
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.
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."
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.
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.
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.
모집단에서 추출된 표본
표본은 전체를 알기 위해 연구하는 한 조각입니다.
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관측 = 간섭 없이 관찰하고 측정함; 실험은 처리를 가함.
알고 싶은 전체 집단은 ___입니다.
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