I will create a 2x2 table to assess the relationship between smoking (exposure) and lung cancer (disease). We will fill the table with numbers, estimate the Relative Risk (RR), Risk Difference (RD), and provide interpretations for each.
Relative Risk (RR) and Risk Difference (RD) Table
| Lung Cancer (+) | Lung Cancer (-) | Total | |
|---|---|---|---|
| Smoking (+) | 100 | 200 | 300 |
| Smoking (-) | 50 | 650 | 700 |
| Total | 150 | 850 | 1000 |
Results Explained
Relative Risk (RR):
- RR measures the likelihood of developing the disease (lung cancer) among those exposed to the risk factor (smoking) compared to those not exposed.
- RR = (Risk of Lung Cancer among Smokers) / (Risk of Lung Cancer among Non-Smokers)
- RR = (100/300) / (50/700) = (1/3) / (7/14) = (1/3) / (1/2) = 1/2.
- So, RR = 0.5
The RR of 0.5 suggests that individuals who smoke are half as likely to develop lung cancer compared to those who do not smoke. In other words, smoking appears to be associated with a decreased risk of lung cancer in this imaginary scenario.
Risk Difference (RD):
- RD measures the absolute difference in risk of disease between exposed and unexposed groups.
- RD = (Risk of Lung Cancer among Smokers) - (Risk of Lung Cancer among Non-Smokers)
- RD = (100/300) - (50/700) = (1/3) - (7/14) = (1/3) - (1/2) = -1/6
- So, RD = -1/6
The RD of -1/6 suggests that there is a 1/6 decrease in the risk of developing lung cancer among individuals who smoke compared to those who do not smoke in this imaginary scenario.
In summary, based on this imaginary data:
- The Relative Risk (RR) indicates that smoking is associated with a decreased risk of lung cancer (RR = 0.5).
- The Risk Difference (RD) indicates that there is a 1/6 decrease in the risk of developing lung cancer among smokers compared to non-smokers.