Table 4– Temporal changes in the prevalence of respiratory outcomes in the four centres (Pavia, Sassari, Turin, and Verona) that participated in at least two surveys

	1998–2000 versus 1991–1993 (ISAYA versus ECRHS)	2007–2010 versus 1998–2000 (GEIRD versus ISAYA)
Current asthma	0.94 (0.79–1.13)	1.38 (1.19–1.59)**
Allergic rhinitis	1.16 (1.07–1.26)**	1.27 (1.19–1.36)**
Wheezing	1.01 (0.90–1.13)	1.18 (1.07–1.28)**
Shortness of breath	0.72 (0.62–0.84)**	1.45 (1.28–1.63)**
Tightness in the chest	0.91 (0.79–1.04)	1.26 (1.13–1.40)**

Data are presented as relative risk (95% CI), obtained through Poisson regression models with robust estimates of the standard errors, adjusting for sex, age, season of response, type of contact (mail/phone) and percentile rank of cumulative response. ISAYA: Italian Study on Asthma in Young Adults; ECRHS: European Community Respiratory Health Survey; GEIRD: Gene Environment Interactions in Respiratory Diseases. **: p≤0.001.