Caution on Assessing Trends in External Causes of Death: Accounting for the Change in 1999 from ICD-9 to ICD-10
The International Classification of Diseases
(exit DHS) (ICD) is a system designed to promote international comparability in the
classification of disease, including reporting causes of death on the death certificate. The most recent change in
ICD codes, from ICD Ninth Edition (ICD-9) to ICD Tenth Edition (ICD-10), was implemented nationwide beginning with
1999 deaths.
It is important for analysts to realize that misleading differences in mortality trends may appear for some
external causes of death because of this change in the classification system. Part of the difference in numbers and
rates of deaths for some conditions between 1998 and 1999 will be due to this change. The coding change may also
mask real changes in mortality rates. See the National Center for Health Statistics discussion
"ICD-10 Framework: External Cause of Injury
Mortality Matrix."
Research by the National Center for Health Statistics provides comparability ratios between the ICD-9 and ICD-10
results for the cause-of-death groups presented in this module. The comparability ratio for a given cause of death
is measured by the net effect of the change in coding systems on the numbers of deaths from that cause. Those
ratios and notes on how to use them are available in a
table of comparability ratios.
Analysts examining mortality trends for any cause of death should check the table to determine how much that cause
is affected by the change in coding system. For each cause of death, the table shows the actual ICD-9 count for
1998 deaths, the estimated number of 1998 deaths if ICD-10 coding was used, and the actual ICD-10 count for 1999
deaths.
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Last Revised: July 29, 2008
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