INFLUENCE OF DEATH CERTIFICATE ERRORS ON CANCER MORTALITY TRENDS

Background: Evaluation of mortality data is an important tool in asses sing both disease time trends and differences in populations. However, the reasons for changes in cancer mortality rates have been controver sial. Questions have been raised concerning whether these increases ar e real or simply the result of changing diagnoses and death certificat e reporting. Purpose: Our purpose was to determine on the basis of aut opsy data if death certificate reporting varies over age, time, and ca ncer type and to explore the effect of death certificate error on rece nt cancer mortality trends. Methods: Data were analyzed from 5886 auto psies collected by the Radiation Effects Research Foundation in Hirosh ima, Japan, between 1961 and 1987. Death certificates were linked to a utopsy data for analyses. An adjustment factor was calculated as a rat io of the accuracy of these death certificates in identifying cancer ( detection rate) and listing cancer (confirmation rate) as the cause of death. This adjustment factor measures bias in mortality rates due to death certification errors and quantifies underestimation and overest imation of cancer mortality rates. Results: Our analyses focused on ly mphoma, breast cancer, neoplasms of the brain, multiple myeloma, and m elanoma because of reported mortality increases. For these cancers, th e adjustment factor decreased significantly (P = .02) over time, imply ing that death certificate accuracy has improved. This change appears to account for 60% of the observed increase in these cancers during th e time period of study. For total cancer, persons 75 years or older ha ve a high adjustment factor but it decreased over time. This decrease suggests an artifactual increase in total cancer mortality rates of ab out 1% per year for this older group. Conclusions: The quality of deat h certificate reporting has generally remained constant for most group s during the period 1961-1987. In the study population, there was a co nsistent underestimation of total cancer mortality of about 18%. For t he five types of cancer studied, there has been less underestimation o f cancer mortality since 1976. For some specific cancers and for perso ns 75 years or older, improvements in death certificate accuracy have occurred over time. These data imply that the total death certificate error rate varies considerably by cancer type, time period, and age at death. Implications: The changes in death certificate reporting for s ome sites and the elderly appear to have artifactually created increas es in cancer mortality rates. These artifacts need to be considered wh en using mortality data for prevention research and health care planni ng.