Lucina finds data about birth defects of limited value unless each specific defect is considered separately. In Norway (Journal of the American Medical Association 2001;285:761–8), 2.5% of the 486 207 boys born between 1967 and 1982 had a birth defect. As might be expected, they were less likely to survive and less likely to have children than boys without a birth defect. Their children had a 6.5-fold increase in risk of the same defect and an 80% increase in risk of a different defect. Nevertheless, affected fathers accounted for only 1.6% of the risk of birth defects in the next generation and affected mothers for only 0.5%.

During the 1996 Olympic Games in Atlanta measures were taken to reduce traffic congestion in the city. These included 24 hour public transport, much expanded park-and-ride services, the banning of private cars from the city centre, and altered work schedules for local businesses. As a result (Journal of the American Medical Association 2001; 285:897–905) peak morning traffic was reduced by 23% and peak daily atmospheric ozone concentrations fell by 28%. At the same time the number of “acute care events” for asthma in children dropped by 11% in two local hospitals and by over 40% as measured by Medicaid claims and on the database of a health maintenance organisation. The reduction in morbidity seemed to be specific …