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Coding causes of death to statistical categories

Introduction to mortality coding tools

Mortality coding is a complex process. Coders are expected to apply and reapply mortality coding rules until the final UCOD can be selected. To correctly select the UCOD, coders need to understand the causal relationships among the conditions reported on death certificates. For each case, the ICD selection and modification rules have to be applied in a logical sequence, beginning with the ‘general principle’ and reapplying the rules until a final UCOD is determined. 

Most countries manually code death certificates, and this can be a slow and costly process, delaying the tion of national mortality statistics by many years. Automating the coding process with coding software can lead to significant improvements in the quality and timeliness of COD data.

Using computerised or paper-based mortality coding tools enables coders to better determine causal relationships, and ensures the consistent application of ICD selection and modification rules, resulting in comparable COD data. These tools also minimise the number of subjective decisions made by coders when selecting the UCOD. Moreover, the use of automated mortality coding reduces the workload for the coders and improves the timeliness of mortality data. It can also reduce the costs for human resources. The US National Center for Health Statistics (Centers of Disease Control and Prevention, CDC) has been a world-wide leader in the field of mortality coding and has developed mechanisms to code data in more-efficient ways. 

An electronic tool currently in use in some countries to facilitate coding and selection of UCOD is Iris, an interactive computer-based system for coding multiple causes of death and selecting UCOD. Iris is a language-independent software system based on the use of national dictionaries and can be operated from a laptop. The main objective of Iris is to increase the quality and comparability of mortality data at the international level. Automated coding systems such as Iris cannot successfully code all causes of death, so manual coding skills will continue to be needed, especially for external causes of death and with complex cases.

Although computerisation can help to overcome numerous problems and speed up the coding process, a computer program cannot be a substitute for an experienced ICD coder. Complex cases as well as external causes of death will still have to be coded manually irrespective of which automated coding tool is used.

Algorithm for application of COD rules

ICD-10 for low-resource settings

WHO has developed a start-up mortality list (SMoL), an automated tool that is in line with the ICD and informs the setting of health priorities and helps track progress towards national and international targets and goals such as the SDGs. This list is designed to be a first step towards standardised reporting of causes of death in low-resource settings, where capacities to code causes of death to three or four ICD digits are lacking.

Although the SMoL is a useful tool for countries in the early stages of ICD implementation, in the longer term all countries will wish to proceed to the use of the more-detailed ICD listing as their skills and capacities for certification and coding improve.

Learn more

The Mortality Medical Data System (MMDS) decision tables were originally developed by the Centres for Disease Control and Prevention (CDC) in 1967 to automated the entry, classification, and retrieval of COD information reported on medical certificates of cause of death in the United States. They are used to help determine the correct UCOD and to assign valid COD codes. The decision tables are available to download for free from:

Iris is an automatic system for coding multiple causes of death and for the selection of the underlying cause of death. The Iris Institute is an international cooperation for the deployment, maintenance and development of the Iris software, which hosts the Iris software and instruction manual: 

A number of WHO-FIC Collaborating Centres regularly offer coding training courses. Contact information for the Collaborating Centres can be found at:

You can access the full ICD-10 training and cause of death certificate version. The site also includes information on the ICD-10 training support group, where those conducting the training can contact expert coders to ask questions

Read more 

Pavillon G (1998). Algorithm for application of Cause of Death rules. Paper prepared for the Meeting of Heads of the WHO Collaborating Centres for the Classification of Diseases. Paris, France. 

Pavillon G et al (2007). Selecting the cause of death on a death certificate. Paper prepared for the WHO Family of International Classifications Network Meeting. Trieste, Italy. 

World Health Organization (2014). The Start-up Mortality List (ICD-10-SMoL) WHO/HIS/HSI/2014.6. 

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