The health-outcome frequencies (mortality,
prevalence, incidence, or person-days) may differ across
countries; thus, national or European data were used
when possible (table 2). For some population
frequencies, rates had to be estimated because of limited
national coverage (hospital admission rates in France
and Switzerland); for others, epidemiological studies
were the only source (bronchitis incidence from the
Adventist Health and Smog Study,13 which has also been
used by Ostro and colleagues14). In these cases, common
baseline frequencies were used for all three countries.