Scientists followed 100 000 adults for 15 years. The table shows the percentage of adults in four groups who developed coronary heart disease.
Table: The percentage of adults who developed coronary heart disease in 15 years, for four groups of adults with different risk factors
| Risk factors present | Percentage (%) of adults who developed coronary heart disease |
|---|---|
| Neither risk factor | 4 |
| Smoking only | 9 |
| High blood cholesterol only | 11 |
| Smoking and high blood cholesterol | 25 |
Calculate how many times more likely an adult with both risk factors was to develop coronary heart disease than an adult with neither risk factor.
The two risk factors together have a greater effect than the sum of their separate effects. Use the data to support this statement.
Suggest why the scientists followed as many as 100 000 adults.
179 exam-style questions on AQA GCSE Biology 2.2 Animal tissues, organs and organ systems, covering 2.2.1 The human digestive system, 2.2.2 The heart and blood vessels, 2.2.3 Blood, 2.2.4 Coronary heart disease: a non-communicable disease, 2.2.5 Health issues, 2.2.6 The effect of lifestyle on some non-communicable diseases, and 2.2.7 Cancer. Each one has a worked solution and a mark scheme showing where the marks go.