Scientists used health records to compare adults who had lived for at least 10 years in two areas. Monitoring showed that one area had a high level of air pollution and the other had a low level of air pollution.
The Table shows the number of adults diagnosed with lung disease.
| Level of air pollution | Number of adults studied | Number diagnosed with lung disease |
|---|---|---|
| High | 800 | 48 |
| Low | 800 | 21 |
Explain two limitations of using this comparison to identify air pollution as the reason for the higher number of lung disease diagnoses.
102 exam-style questions on Edexcel GCSE Biology 5.4 Non-communicable diseases, covering 5.4.1 Interaction of factors in non-communicable disease, 5.4.2 Lifestyle factors and non-communicable disease, and 5.4.3 Treatments for cardiovascular disease. Each one has a worked solution and a mark scheme showing where the marks go.