Figure 2

FEV ₁ of healthy individuals and smokers. (a): FEV₁ measurements (in litres) of healthy individuals (Group H, blue) and smokers (Group S, red). (b): Mean change of FEV₁ for healthy individuals and smokers over ages. To enforce smoothness, each mean value is calculated over an age interval of 11 years (the X-axis labels indicate the ages at the middle of the intervals). (c): Estimated average decline of FEV₁ for healthy individuals and smokers of average height (1.62 metres) using the model defined by (1). (d): Biological ageing of smokers relative to healthy individuals inferred from (c) using as definition of biological age the chronological age of healthy individuals with equal lung function mean.