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Comparability Ratio
About every 10-20 years the International Classification of Diseases (ICD) is revised to stay abreast of advances in medical science and changes in medical terminology. Each of these revisions produces breaks in the continuity of cause-of-death statistics. Discontinuities across revisions are due to changes in classification and rules for selecting underlying cause of death. Classification and rule changes impact cause-of-death trend data by shifting deaths away from some cause-of-death categories and into others. Comparability ratios measure the effect of changes in classification and coding rules. For causes shown in Table VI, comparability ratios range between 0.6974 and 1.1404. Influenza and pneumonia had the lowest comparability ratio (0.6974), indicating that Influenza and pneumonia is 30% less likely to be selected as the underlying cause-of-death in ICD-10 than in ICD-9. Pregnancy, childbirth, and the puerperium had the highest comparability ratio (1.1404), indicating that pregnancy is more than 14% more likely to be selected as the underlying cause using ICD-10 coding.
For selected causes of death, the ICD�codes used to
calculate death rates for 1980 through 1998 differ from the
ICD�codes most nearly comparable with the corresponding
ICD� cause-of-death category, which also affects the ability
to compare death rates across ICD revisions. Examples of
these causes are ischemic heart disease; cerebrovascular
diseases; trachea, bronchus and lung cancer; unintentional
injuries; and homicide. To address this source of discontinuity,
smortality trends for 1980�98 were recalculated, using
ICD�codes that are more comparable with codes for
corresponding ICD� categories.
Table V shows the ICD�/p>codes used for these causes. Although this modification may
lessen the discontinuity between the Ninth and Tenth
Revisions, the effect on the discontinuity between the Eighth
and Ninth Revisions is not measured.
Comparability ratios shown in
Table VI are based on acomparability study in which the same deaths were coded by
both the Ninth and Tenth Revisions. The comparability ratio
was calculated by dividing the number of deaths classified by
ICD� by the number of deaths classified by ICD� The
resulting ratios represent the net effect of the Tenth Revision
on cause-of-death statistics and can be used to adjust
mortality statistics for causes of death classified by the Ninth
Revision to be comparable with cause-specific mortality
statistics classified by the Tenth Revision.
The application of comparability ratios to mortality statistics
helps make the analysis of change between 1998 and 1999
more accurate and complete. The 1998 comparability-modified
death rate is calculated by multiplying the comparability ratio
by the 1998 death rate. Comparability-modified rates should
be used to estimate mortality change between 1998 and
1999.
Caution should be taken when applying the comparability
ratios presented in
Table VI to age-, race-, and sex-specificmortality data. Demographic subgroups may sometimes differ
with regard to their cause-of-death distribution, and this would
result in demographic variation in cause-specific comparability
ratios.
SOURCE: Health, United States
Related
Links
Comparability
of Cause of Death Between ICD-9 and ICD-10
National Vital
Statistics Reports
(Vol. 49 No. 2 and Vol. 49 No. 3)
Cause of Death
International
Classification of Diseases
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This page last reviewed
January 11, 2007
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