In order to interpret data on long-term time trends in asthma mortality, it is necessary to firstly review the key issues
of the accuracy of death certification, disease classification and diagnostic fashion. As the diagnosis of asthma as the cause
of death is firmly established in the 5–34-year age group [1–6], long-term trends in asthma mortality within countries and
comparisons between countries are normally confined to this age group. Although most deaths occur in the older age group,
the accuracy of asthma as the cause of death declines with increasing age due to confounding with other respiratory disorders
such as chronic obstructive pulmonary disease (COPD) or the presence of intercurrent medical conditions.
Changes in disease classification coding are also relevant, with the International Classification of Diseases (ICD) implementing
major revisions in the coding of asthma. The ICD revisions occur about every 10 years, usually involving the manner in which
deaths due to asthma and bronchitis are coded. These revisions usually have minimal effect on the coding in the 5–34-year
age group [7–11].