What is an ecological study and what is a common ecological fallacy risk?

• A. They analyze data at the group level; risk of inferring individual-level associations from group-level data.
• B. They analyze data at the individual level; ecological fallacy occurs due to sampling bias.
• C. They are experiments conducted at the community level; ecological fallacy is randomization error.
• D. They rely on laboratory measurements of exposure.

Answer: (C)