Practise identifying observational studies, naming their variables, recognising possible confounding, and explaining why observed association does not establish causation.
A car maker produces four different models of cars: A, B, C, and D. A group of researchers is investigating which model of car has the longest distance traveled per gallon of gas (mileage). Higher mileage is considered better than lower mileage. The researchers will conduct a study in which they contact several owners of each model of car and ask them to estimate their mileage.
Is this an observational study or an experiment? Justify your answer in context.
This is an observational study. The researchers had the car owners estimate their mileage. The car owners were not randomly assigned a car model, so no treatment was imposed.
Essentially correct (E) if the response satisfies the following three components:
2. Provides a justification based on no treatment being imposed
Partially correct (P) if the response satisfies only two of the three components required for E.
Incorrect (I) if the response does not meet the criteria for E or P.
Additional Notes:
- A response that states the study is an experiment receives a score of I for part (a).
- A response that states "No random assignment of treatment" may satisfy component 2.
- A response may satisfy component 3 with car models, drivers, cars, owners, or members. Mileage alone does not satisfy component 3.