In a follow -up study, Goren and Hellmann [23] evaluated changes in the prevalence rates of asthma among schoolchildren (aged 13–14) during the period 1980–1989. In their study, air pollution levels were determined according to concentrations of SO2 and NOx, counted as the total number of air pollution events during which half-hour averages of SO 2 or NOx were above an arbitrary threshold, set as one-quarter of the local air quality pollution standards (183 mg/m3 for SO2 and 235 mg/ m3 for NO x). During the study period, a significant increase in asthma prevalence occurred among fifth-grade children in all the communities under analysis: odds ratio (OR) 1.79, 95% confidence interval (CI) 1.16–2.74, P < 0.01. A significant increase in the prevalence of wheezing, accompanied by short-ness of breath, was also observed (OR 1.759, 95%CI 1.11–2.28, P < 0.05). However, the authors could not attribute the prevalence of asthma to environmental variables, concluding that the main reason for the increase in asthma and related respiratory symptoms remained unclear.