<qa>  What is the basic spirometry performed on each occasion?The investigators recruited volunteers through a newspaper and television campaign, that provided information about the study design and eligibility criteria. The participants were asked to sign written informed consent to randomization in one of the two groups. Upon arrival, subjects were given a questionnaire to be completed and returned before leaving the centre. It includes a brief personal and family medical history, smoking details and information about attempts and assistance to stop smoking. A blood sample is collected from each subject at baseline and every two years follow-up. A basic spirometry is performed on each occasion. 