As of 2015, the ninth revision of the International Classification of Diseases, ICD-9, provides consistency in the classification of deaths between 1979 and 1998 for use in mortality statistics. Classification of disease in living patients occurs based on the revision of the ICD considered current at the time of diagnosis.
The ICD provides a translation method for linking conditions and diseases to specific, established codes using the defined selection and modification rules included in the applicable ICD revision. The use of a common classification system allows for the systematic selection of a single cause of death, known as the underlying condition. Secondary, contributing causes are labeled as non-underlying conditions. The combination of the underlying condition and any non-underlying conditions is known as multiple causes of death. The specificity ingrained in this system simplifies statistical calculations regarding epidemiology, mortality and morbidity.
The ICD is published by the World Health Organization and undergoes a periodic, collaborative revision process to incorporate advances in the health sciences and medical practices fields. WHO member states use the ICD to provide consistency and comparability in the data collected from disparate population groups. Researchers, health care providers, health information managers, insurers and policymakers use the ICD to classify disease on health and death records.