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

1. A

   Case control study

2. B

   Cohort study

3. C

   Cross sectional study

4. D

   Ecological study

Appeared in: NORCET 10 Prelims-2026

Explanation

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• Ecological study because the unit of analysis is a population or group (in this case, nations), not individuals.
• The study compares aggregate measures of exposure (per capita tobacco consumption) and outcome (national COPD prevalence) across these groups.
• This design is used to look for associations between exposure and disease at a population level, often as a first step in exploring a potential link.

Why Other Options Were Wrong

• Option A: A case-control study is incorrect because it starts with individuals who have a disease (cases) and compares their past exposures to individuals without the disease (controls). The question describes a study using population-level data.
• Option B: A cohort study is incorrect because it follows groups of individuals over time to observe who develops an outcome. The study in the question does not follow individuals; it analyzes existing national statistics.
• Option C: A cross-sectional study is incorrect because, while it measures exposure and outcome at the same time, its unit of analysis is typically the individual. The study described uses aggregate data for entire nations.

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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.
• Ecological studies are often the first step in epidemiological research because they can be done quickly and inexpensively using existing data.
• They are valuable in public health for identifying large-scale trends and generating hypotheses that can be tested later with more rigorous (and expensive) individual-level studies like cohort or case-control studies.
• What if the study had instead recruited 10,000 smokers and 10,000 non-smokers and followed them for 10 years to see who developed COPD? In that case, the design would be a prospective cohort study, which provides much stronger evidence for a causal link.

How to Approach the Question

• First, identify the core components of the study described in the question: What is being measured, and in whom?
• Notice the keywords: '15 nations', 'per capita', and 'national prevalence'. These all point to data being analyzed at a group or population level, not at an individual level.
• Recall the definitions of the main epidemiological study designs.
• A case-control study compares individuals with and without a disease.
• A cohort study follows individuals over time.
• A cross-sectional study assesses individuals at a single point in time.

Concept Tested & Keywords

• Concept Tested: Epidemiological Study Designs
• Stem keywords: 15 nations, per capita tobacco consumption, national COPD prevalence, positive correlation
• Lead-in keywords: Which study type
• Clinical cues: The use of aggregate data ('15 nations', 'per capita', 'national prevalence') is the defining feature pointing to an ecological study.

Question ID

QLpNMJhJAVqExlS7rgQKfD

Copy ID

Reference Book

E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart A (pp 26-201 of 604) pp. 64-66, 62-64

E6 NursingResearch Suresh Sharma 5e Part 1 p. 186-188