A study of a new memory drug recruits 200 volunteers. Volunteers are split by age (under 50, 50+). Within each age group, half are randomly assigned to the drug and half to a placebo. Neither subjects nor evaluators know assignments. Memory test scores are compared.
What is the most appropriate scope of inference if the drug group scores significantly higher?
- Acheck_circle
Causal inference for the volunteers (similar profile), but limited generalization since they were not randomly sampled
- B
Generalization to the population but no causal claim
- C
Neither causal nor generalizable conclusions are justified
- D
Causal inference for all adults nationally
Explanation
Random assignment within blocks supports causation for these subjects. Volunteers were not randomly sampled, so generalization beyond similar individuals is not justified by the design.