Health data from 15 nations investigating the relationship between per capita tobacco consumption and national COPD prevalence, revealing a strong positive correlation. Which study type best describes this?

1. A

   A. Case-control study

2. B

   B. Cohort study

3. C

   C. Cross-sectional study

4. D

   D. Ecological study

Appeared in: INI-CET EXAM -2026

Explanation

• An ecological study is the correct choice because its unit of analysis is a population or group, not an individual.
• The question describes a study comparing data from '15 nations,' which are populations.
• It analyzes aggregate data, such as 'per capita' consumption and 'national' prevalence, to find correlations at the group level.
• This design is often used to generate hypotheses about potential risk factors by looking at large-scale trends.

Why Other Options Were Wrong

• Option A: A case-control study is incorrect because its unit of analysis is the individual. It compares people who already have a disease (cases) with people who do not (controls) and looks backward in time to compare past exposures.
• Option B: A cohort study is incorrect because it follows groups of individuals over time to see who develops a disease. The unit of analysis is the individual, and the direction is forward from exposure to outcome.
• Option C: A cross-sectional study is incorrect because, while it can provide a 'snapshot' in time, its primary unit of analysis is the individual. It measures both exposure and outcome at the same time in a group of individuals.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Epidemiological study designs as background academic context rather than a clinical decision trigger.
• Understanding different study designs is fundamental to evidence-based nursing practice, allowing nurses to critically appraise research articles and apply the best available evidence to patient care.
• Nurses must be aware of the limitations of each study type, such as the ecological fallacy in ecological studies, to avoid making incorrect assumptions about individual patients based on population-level data.
• What if? If the study had recruited 10,000 smokers and 10,000 non-smokers and followed them for 20 years to record who developed COPD, the design would change to a cohort study because it tracks individuals from exposure to outcome over time.

How to Approach the Question

• First, identify the unit of analysis in the study described. The question explicitly mentions '15 nations' and uses population-level data like 'per capita' consumption and 'national' prevalence.
• Recognize that the study is analyzing groups (populations), not individual people.
• Next, review the definitions of the study types provided in the options.
• A case-control study, cohort study, and cross-sectional study all primarily use the individual as the unit of analysis.
• An ecological study is defined by its use of population-level data to look for associations.
• Conclude that since the study analyzes data at the national level, it is an ecological study.

Concept Tested & Keywords

• Concept Tested: Epidemiological study designs
• Stem keywords: 15 nations, per capita tobacco consumption, national COPD prevalence, correlation
• Lead-in keywords: Which study type

Question ID

Q1u4mwO3a0QUIDdA847WVN

Copy ID

Reference Book

E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart A (pp 26-201 of 604) p. 64-66