Importantly, the cause of death is also recorded after multiple
validation checks. We classify causes of death as either cardiorespiratory
or noncardiorespiratory. The cardiorespiratory causes of
death that are those that have been linked to ambient air quality
and include heart disease (17), stroke (18–20), lung cancer (21),
and respiratory illnesses (22, 23). Causes of death presumably
unrelated to air quality include other cancers, accidental or violent
deaths, and various stomach ailments. Together, these two categories
cover all causes of death.