Interpreting Data on the Cardiovascular System (AQA A Level Biology): Revision Note

While you will not be asked to list risk factors or explain the development of CVD, you may be asked to interpret data relating to the connection between CVD and a particular risk factor.

A study was carried out into the relative risk of CVD in non-smoking adults exposed to a range of levels of cigarette smoke from a smoking partner.  The study looked at 523 non-smoking partners of smokers. 

(a) Describe what the data show about the link between smoke exposure and CVD risk.

[2]

(b) State what can be concluded about the link between smoke exposure and CVD risk.

[1]

(c) Comment on the validity of the data.

[3]

Answer:

(a) A description of this data could include the following:

Any two of the following:

• As the number of cigarettes smoked per day increases, the relative risk of CVD increases; [1 mark]

• Non-smokers exposed to 0 cigarettes per day have no increased risk of CVD / have a relative risk of 1.00; [1 mark]

• Non-smokers exposed to 20 or more cigarettes per day have the highest risk of CVD AND they have a relative risk of 1.31; [1 mark]

(b) A conclusion from the data could be:

• There is a correlation / association between increased exposure to cigarette smoke and an increased risk of CVD; [1 mark]

(c) A commentary on the validity of the data could include:

Any three of the following:

• 523 people is a fairly small sample size and may not represent an entire population; [1 mark]

• More studies would need to be carried out to back up these results; [1 mark]

• There is no information on how other risk factors might be interacting with smoking OR risk factors such as age / diet / biological sex / exercise levels may be affecting the results; [1 mark]

• The data doesn't use any statistical tests so we cannot state the significance of the differences between the different levels of smoke exposure; [1 mark]

Note that part (b) above draws attention to a common area of confusion; that of correlation vs causal relationship. It would not be correct here to say that increased smoke exposure causes an increased risk of CVD; instead we can only say for sure that there is a correlation, or association, between the two variables.