A teacher wants to test whether a new study app improves test scores. She has 40 students use the app and measures their improvement from a pretest to a posttest.
What is the most important missing element of this experiment?
- Acheck_circle
A control group not using the app
- B
Stratification by gender
- C
A larger sample size
- D
Voluntary response
Explanation
Without a control group, improvement cannot be attributed to the app rather than to retesting, normal learning, or other factors. A control group is essential for comparison.