Question

question what is the main difference between observational studies and experiments? ∘ experiments take place in a lab while observational studies do not need to. ∘ in an observational study we only look at what happened in the past. ∘ most experiments use random assignment while observational studies do not. ∘ observational studies are completely useless since no causal inference can be made based on their findings. submit

Explanation:

• Analyze each option:
• Option 1: Experiments can be done outside labs (e.g., field experiments) and observational studies can be in labs, so this is incorrect.
• Option 2: Observational studies can be prospective (looking at current/future) or retrospective, not only past, so incorrect.
• Option 3: In experiments, random assignment to groups is common to establish causality, while observational studies observe existing groups without manipulating or randomly assigning, so this is correct.
• Option 4: Observational studies are useful for associations and in cases where experiments are unethical, so "completely useless" is wrong.

Answer:

C. Most experiments use random assignment while observational studies do not.