Note: The underlying cause of death is the condition giving rise to the chain of events leading to death. Between January 1, 1979 and December 31, 1998, the underlying causes of death were classified in accordance with the Ninth Revision of the International Classification of Diseases (ICD-9), a coding structure developed by the World Health Organization. Starting January 1, 1999, causes of death were classified using the Tenth Revision of the International Classification of Diseases (ICD-10). With each revision there are differences in classifying the underlying cause of death. Therefore, health statistics based on one revision are not directly comparable to the other revision without the use of comparability ratios.

The asterisk (*) preceding the "U" codes for homicide and suicide indicates codes that were introduced by the United States to classify deaths due to terrorism, but which are not officially part of the WHO’s ICD code book.

The comparability ratio results from double-coding a large sample of the national mortality file, once by the old revision (ICD-9) and again by the new revision (ICD-10), and expressing the results of the comparison as a ratio of deaths for a cause of death by the later revision divided by the number of that cause of death coded and classified by the earlier revision. A ratio greater than 1.0 indicates that the new coding structure will classify more deaths to that underlying cause of death.

See the National Center for Health Statistics for more information on the comparability ratio and the classification of mortality.

⁽¹⁾Between 1999-2008, pneumonia & inflenza were grouped using ICD-10 codes J10-J18.