Experimental vs. observational study
Decide whether a physiology study changed a condition on purpose (experimental) or just watched and recorded (observational).
- Independent variable: An experiment requires a factor the researcher sets on purpose; spotting that factor is what separates the two study types.
- Control group vs. comparison group: Experiments assign people to groups and apply a treatment; knowing what assignment means anchors why a study counts as experimental.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
An experimental study applies a treatment the researcher controls; an observational study only watches and records what people already do.
A team measures the resting heart rate of students who already exercise daily and students who do not, and compares the two groups. No one is told to change anything. Which study type is this?
Reviewed- A.Experimental, because two groups are compared
- B.Experimental, because heart rate is measured
- C.Observational, because the team only records existing habits
- D.Observational, because heart rate cannot be controlled
Show the worked solution ▾
Answer: C. Observational, because the team only records existing habits
- Step 1: Check for a treatment: No one was told to start or stop exercising; the team applied nothing.
- Step 2: Name what happened: The team only measured and recorded what students already did, so it is observational.
Why it's right: The team changed nothing and only recorded existing exercise habits, which is the definition of an observational study.
- A: Comparing two groups happens in observational studies too; comparison alone does not make it experimental.
- B: Measuring heart rate is just collecting data, which both study types do.
- D: The reason it is observational is that no treatment was applied, not anything about controlling heart rate.
Aligned to BI 2.1: experimental vs. observational · reading level ~grade 9
- A wearable-device company that records steps from millions of users who already wear the watch is running an observational study: it never told anyone how much to walk.
Fill these in as you work through the lesson.
- Experimental study (the researcher does something on purpose):
- Observational study (the researcher only watches):
- Treatment (the thing applied to one group):
- Assign (the researcher decides who is in which group):
If the researcher decides who gets the treatment and applies it, the study is . If the researcher only records what people already do, the study is .
- A team gives half of a class a new sports drink before a run and gives the other half water, then measures heart rate. Which study type is this and how do you know?
- A team records the resting heart rate of students who already drink coffee and students who already do not, and compares them. Which study type is this?
- What one action turns a study from observational into experimental?
A researcher wants to know if standing up changes blood pressure. Describe one way to run it as an experimental study and one way to run it as an observational study.