Technical Appendix

This appendix explains some of the sources and methods used by the National Safety Council (NSC) Statistics Department in preparing the estimates of deaths, injuries, and costs. Many of the estimates depend on death certificate data provided by the National Center for Health Statistics (NCHS). Here is a brief explanation of the certification and classification of deaths.

Certification and classification

The medical certification of death involves entering information on the death certificate about the disease or condition directly leading to death, antecedent causes, and other significant conditions. The death certificate is then registered with the appropriate authority, and a code is assigned for the underlying cause of death.

The underlying cause is defined as “(a) the disease or injury which initiated the train of morbid events leading directly to death, or (b) the circumstances of the accident or violence which produced the fatal injury” (World Health Organization [WHO], 1992). Deaths are classified and coded on the basis of a WHO standard, the International Statistical Classification of Diseases and Related Health Problems, commonly known as the International Classification of Diseases or ICD (WHO, 1992).

For deaths due to injury and poisoning, the ICD provides a system of “external cause” codes to which the underlying cause of death is assigned. Visit this page and click on “Data Table” for a condensed list of external cause codes.

Comparability across ICD revisions

The ICD is revised periodically, and these revisions can affect comparability from year to year. The sixth revision (1948) substantially expanded the list of external causes and provided for classifying the place of occurrence. Changes in the classification procedures for the sixth revision, as well as the seventh (1958) and eighth (1968) revisions, classified as diseases some deaths previously classified as injuries.

The eighth revision also expanded and reorganized some external cause sections. The ninth revision (ICD-9,1979) provided more detail on the agency involved, the victims’ activity, and the place of occurrence. The tenth revision (ICD-10), which was adopted in the United States effective with 1999 data, completely revised the transportation-related categories. Specific external cause categories affected by the revisions are noted in the historical tables.

This table lists the ICD-9 codes, the ICD-10 codes and a comparability ratio for each of the principal causes of unintentional-injury death. The comparability ratio represents the net effect of the new revision on statistics for the cause of death. The comparability ratio was obtained by classifying a sample of death certificates under both ICD-9 and ICD-10 and then dividing the number of deaths for a selected cause classified under ICD-10 by the number classified to the most nearly comparable ICD-9 cause. A comparability ratio of 1.00 indicates no net change due to the new classification scheme. A ratio less than 1.00 indicates fewer deaths assigned to a cause under ICD-10 than under ICD-9. A ratio greater than 1.00 indicates an increase in assignment of deaths to a cause under ICD-10 compared to ICD-9.

The broad category of “accidents” or “unintentional injuries” under ICD-9 included complications and misadventures of surgical and medical care (E870-E879) and adverse effects of drugs in therapeutic use (E930-E949). These categories are not included in “accidents” or “unintentional injuries” under ICD-10. In 1998, deaths in these two categories numbered 3,228 and 276, respectively.

Under ICD-9, the code range for falls (E880-E888) included a code for “fracture, cause unspecified” (E887). A similar code does not appear in ICD-10 (W00-W19), which probably accounts for the low comparability ratio (0.8409). In 1998, deaths in code E887 numbered 3,679.

Beginning with 1970 data, tabulations published by NCHS no longer include deaths of nonresident aliens. In 2016, there were 1,045 such unintentional deaths, of which 324 were motor-vehicle related.