Statistics / Unit 5: Collecting Data
5.4 Observational Studies vs Experiments
Notes
- In an observational study, researchers observe and record data without imposing treatments.
- In an experiment, researchers deliberately impose treatments on experimental units (subjects) and measure the response.
- A confounding variable is related to both the explanatory variable and the response, so its effects cannot be separated. A lurking variable is a similar hidden variable.
- Only experiments with random assignment can show cause and effect.
- Example: Comparing people who choose to take vitamins to those who do not is observational, since healthier habits may be confounded with taking vitamins.
Practice
Researchers compare the health of people who choose to take a vitamin with the health of people who do not. This is:
The researchers did not assign who takes the vitamin.
What makes a study an experiment?
Imposing treatments is the key feature of an experiment.
A study finds coffee drinkers have more heart disease, but coffee drinkers also smoke more. Smoking is a:
Smoking is related to both coffee drinking and heart disease, so the effects are mixed together.
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