In the accompanying randomised controlled trial, Parkes and colleagues assess the effect of telling patients over 35 years of age their estimated spirometric lung age as an incentive to quit smoking.1 Support for conducting the trial comes from a recent Polish observational study on the potential association between smoking cessation and participants’ spirometry results, as communicated using Fletcher and Peto’s diagram (a pictorial representation of how smoking ages the lungs).2 The Polish study showed higher smoking cessation rates at one year in smokers with airway obstruction than in those with normal spirometric parameters. However, the study had no control group without spirometry testing or without feedback on such testing. The authors called for a large randomised controlled trial comparing the effect of providing spirometry results versus no spirometry results on smoking cessation.

In Parkes and colleagues’ trial, participants in the intervention group received comprehensive information about their spirometry results including individualised interpretation, …