Question

A researcher wanted to prove the relation between COPD and smoking. He collected patient records from government hospitals and records of cigarette sales from the finance and taxation department. This is an example of which study design?

• A. Cross-sectional study
• B. Posological study
• C. Ecological study
• D. Operations research

Hint:

The data are at population level, not on individual patients.

Answer 1

The Correct Option is C

Quick rule: when the exposure and the outcome are both counted for a whole group and never matched person to person, the design is ecological.
Here cigarette sales (the exposure) come from a tax department total, and COPD numbers (the outcome) come from pooled hospital records. No single person is recorded as both a smoker and a COPD case, so the correlation is drawn at population level. That is the defining feature of an ecological correlation study.
Eliminate the rest fast: a cross-sectional study needs both exposure and disease measured in the same individuals at one time point. Operations research studies the working of a programme to fix bottlenecks. A posological study is about dose. Since only aggregate population figures are compared, ecological study is the fit.
Watch the trap of ecological fallacy: a group-level link does not prove the same link holds in individuals. Ref: Park PSM, 24e.