A5. Interpreting Lung Disease Data

Question 1

Describe the data
Draw conclusions
Other points to consider?

Answer 1

Describe the data:
Figure 1 shows that the number of adult males in Great Britain who smoke decreased between 1990 and 2012. Figure 2 shows that the male lung cancer mortality (death) rate decreased between 1990 and 2012 in the United Kingdom.

Draw conclusions:
You need to be careful what you say here. There’s a correlation (link) between the number of males who smoked and the mortality rate for male lung cancer. But you can’t say that one caused the other. There could be other reasons for the trend, e.g. deaths due to lung cancer may have decreased because less asbestos was being used in homes (not because fewer people were smoking).

Other points to consider:
Figure 2 shows mortality (death) rates. The rate of cases of lung cancer may have been increasing but medical advances may mean more people were surviving (so only mortality was decreasing, not the number of people developing the disease).

Question 2

Describe the data
Draw conclusions
Other points to consider?

Answer 2

Describe the data:
Figure 3 shows that the number of new cases of asthma in the UK fell between 1996 and 2000, from 87 to 62 per 100 000 people.
Figure 4 shows that the emissions of sulfur dioxide in the UK fell between 1996 and 2000, from 2 to 1.2 million tonnes.

Draw conclusions:
Be careful what you say when drawing conclusions. Here there’s a link between the number of new cases of asthma and emissions of sulfur dioxide in the UK-the rate of new cases of asthma has fallen as sulfur dioxide emissions have fallen. You can’t say that one causes the other though because there could be other reasons for the trend, e.g. the number of new cases of asthma could be falling due to the decrease in the number of people smoking. You can’t say the reduction in asthma cases is linked to a reduction in air pollution (in general) either as only sulfur dioxide levels were studied.

Other points to consider:
Figure 3 shows new cases of asthma. The rate of new cases may be decreasing but existing cases may be becoming more severe. The emissions were for the whole of the UK but air pollution varies from area to area, e.g. cities tend to be more polluted. The asthma data doesn’t take into account any other factors that may increase the risk of developing asthma, e.g. allergies, smoking, etc.