time between the first and second survey for non asthmatics and the time between the first interview and the first asthma attack for new asthmatics. For 6 subjects, who reported in the second survey having had the first attack of asthma less than 3 years before the first survey, the time at risk was set at 1 day \[[@B4]\].

Subjects, reporting in the first study, having had \'wheezing or whistling in their chest at any time\' and/or having \'woken up with a feeling of tightness in the chest\' and/or having \'woken up with an attack of shortness of breath\' in the past 12 months, were considered as having asthma symptoms at baseline.

All subjects who reported never having smoked in the second questionnaire were considered non smokers at baseline. Subjectsand in recent generations.

ii\) The presence of asthma attacks and nocturnal asthma symptoms (tightness and dyspnoea) in young adults is associated with a two-fold increase in the risk of dying in the subsequent seven years, compared to asymptomatic subjects.

Incidence
---------

In our analysis of the incidence of asthma, the population at risk and the new cases of the disease were defined according to the occurrence or absence of a relevant clinical event, such as an asthma attack, which is less likely to be influenced by recall bias and more reproducible than the reporting of asthma symptoms \[[@B15],[@B16]\]. It has also been reported that, at least in Italy, the large majority (85%) of subjects who self-reported an attack of asthma had been diagnosed by a doctor \[[@B1]\]. Consequently, it is likely