A study followed four groups of workers for 10 years. The groups had the same age distribution.
| Smoking | Ionising radiation exposure | Number of workers | Number who developed cancer |
|---|---|---|---|
| no | lower | 4000 | 20 |
| no | higher | 3000 | 24 |
| yes | lower | 2500 | 25 |
| yes | higher | 2000 | 30 |
Compare the apparent contribution of higher ionising radiation exposure to cancer risk in workers who smoked and workers who did not smoke. Use calculations in your answer.
Suggest one reason why this study cannot establish a cause-and-effect relationship between ionising radiation exposure and cancer.
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.