THE International Classification of Diseases and Causes of Death (ICD) is revised at approximately ten-year intervals, and considerable regrouping of diagnostic categories may occur at the time of these revisions. It has, therefore, become common practice for offices of vital statistics to publish "adjustment factors" by which mortality from a particular cause of death may be followed from one revision into the next without an abrupt and potentially misleading change in rate due to the altered method of bookkeeping.
Unfortunately, if used inappropriately, the adjustment factors may themselves lead to erroneous conclusions about changes in death rates. Since another revision of the ICD will soon be introduced, it is important that the limitations of these adjustment factors be recognized.
Our interest in the subject was aroused by an article published in JAMA in 1974,1 in which the author questioned the widespread belief that mortality from coronary heart disease was
Halliday ML, Anderson TW. Adjustment Factors in Mortality Statistics: A Word of Caution. JAMA. 1977;238(19):2025–2026. doi:10.1001/jama.1977.03280200037013
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