The international comparability of cancer mortality data. Results of an international death certificate study

In preparation for the 10th revision of the International Classification of Diseases (ICD-10), a two-part study was undertaken to assess the international comparability of the coding, by the 9th revision (ICD-9), of death certificates mentioning cancer, to see whether there had been improvement since the 8th revision (ICD-8). Part I repeated a 1978 study in which nine countries coded the same 1,234 United States death certificates mentioning cancer by ICD-9. The proportion of disagreements in coding the underlying cause of death fell about 35% between 1978 and the present study. This reduction was probably due to the new more detailed rules for coding cancer death certificates given in ICD-9. To combat the criticism of the possible bias associated with using United States death certificates only, in Part II of the study, each of seven countries submitted about 100 certificates translated into English which had posed problems in coding cancer. Discrepancies in assigning the underlying cause of death were found for 54% of these problem certificates. The major types of problems identified were coding when multiple cancer sites were mentioned on the death certificate, whether to select heart disease or cancer as the underlying cause of death, and the interpretation of the coding rules. Better rules for ICD-10 must be provided for both physicians and coders if international comparability of cancer mortality data is to be achieved.