Comparison of the coding of death certificates related to cancer in seven countries.

Abstract

INTERNATIONAL MORTALITY STATISTICS have been derived for many years from information recorded in the medical certification portion of death certificates that have been coded in accordance with the International Classification of Diseases (ICD). The ICD, which was initially published in 1900 and has undergone decennial revisions, includes not only a detailed classification of diseases, injuries, and external causes of death but also international coding rules for selecting the underlying cause of death. Good mortality data depend on accurate and consistent coding of death certificates. Such accuracy means that all diagnostic statements about the same disease or condition, no matter how imprecise or poorly expressed, are given the same code number by different coders. There is no advantage in having an international classification for coding the causes of mortality if the rules for coding are applied so differently that the resulting statistics are not comparable. During the previous decennial revisions of the ICD, the World Health Organization (WHO) attempted to evaluate the application of the ICD coding rules (1). When WHO planned for the ninth revision-ICD-9 (2), a subcommittee on oncology was constituted to prepare a special supplement on cancer-ICD-O, the International Classification of Diseases for Oncology (3). In addition to preparing ICD-O, this subcommittee studied the actual interpretations given to the coding rules pertaining to cancer and the resulting effect on cancer mortality statistics. In this paper we describe a research project undertaken to evaluate the use on the rules of the eighth (1965) revision-ICD-8 (4), especially as applied to neoplasms. The problems we found, and also proposed solutions that were the basis for the pertinent ICD-9 rules, are presented. The ICD-9 has a new section (VI) on ground rules for malignant neoplasms that provides much more guidance on their coding than ICD-8, which devotes only a brief paragraph (V) to the coding of malignant neoplasms of multiple sites.