Limitations of the death certificate only index as a measure of incompleteness of cancer registration.

The death certificate only (DCO) index, which quantifies the proportion of patients for whom the death certificate provides the only notification to the registry, is a widely used measure of incompleteness of population-based cancer registration. This paper provides an algebraic assessment and a quantitative illustration of the relationship between the DCO index and incompleteness of cancer registration. It is shown that the relationship between the DCO index and incompleteness of registration is strongly dependent on the case fatality rate and the misclassification rates of cancer deaths among unregistered patients. Therefore, the DCO index is a very poor indicator of incompleteness. Similar limitations apply to the DCN index (proportion of cases first notified by death certificate), which has been proposed as an alternative measure of incompleteness.