Researchers observe that students who sleep more tend to earn higher grades. Which conclusion is justified?
- More sleep definitely causes higher grades.
- Sleep and grades are associated in the observed group.
- Higher grades cause students to sleep.
- The study proves every student needs the same sleep.
Show answer and explanation
Answer: Sleep and grades are associated in the observed group.
An observational study can show association, but other variables prevent a definite causal conclusion.