Valid, reliable, and comparable assessments of trends in causes of death are limited by a number of factors. Changes in cause of death coding over time make it difficult to compare deaths assigned with different versions of coding systems. In addition, deaths are frequently assigned codes that are not useful for public health analyses, often called garbage codes.
New algorithms have been developed to redistribute cause of death coding for deaths that have been improperly classified. These new algorithms allow for more effective large-scale comparisons of cause of death trends across countries and time. In the study, Algorithms for enhancing public health utility of national causes-of-death data, researchers built on prior cause of death analysis work and created a more detailed approach to these problems.
The fraction of all deaths assigned to garbage codes varied tremendously across countries and revisions of the International Statistical Classification of Diseases and Related Health Problems (ICD), which provides codes to classify health conditions. In general, across all country-years of data available, garbage codes have declined from more than 43% in the seventh revision of the ICD (ICD-7) to 24% in ICD-10.
Garbage codes also varied by region and age group. In some regions, such as Australasia, garbage codes in 2005 were as low as 11%, while in some developing countries, such as Thailand, they were greater than 50%. Across different age groups, the composition of garbage codes varied widely, with most types of garbage codes increasing with age.
Mapping causes of death through different ICD versions and redistributing garbage codes enhances the public health utility of cause of death data. The researchers believe that these new methods will lead to an increased demand for higher-quality cause of death data from health sector decision-makers.
Researchers looked at cause of death data from 145 countries from 1901 to 2008 and developed a public-health oriented cause of death list. The resulting 56 causes of death were mapped from ICD-6 to ICD-10, and where possible, they have also been mapped to the International List Causes of Death 1-5. Researchers consulted with Global Burden of Disease experts to identify likely causes to which garbage codes should ideally be reassigned. Practical algorithms to redistribute the deaths were developed and applied to a database of more than 700 million deaths.
The variable use of garbage codes across countries and over time profoundly limits meaningful comparisons of causes of death. This study is part of ongoing work by IHME to enhance the utility of national cause of death data for public health analysis and to better understand the current state of population health.
Recommendations for future work
The results of this study indicate that these algorithms can be generally applied to country-level data by analysts interested in comparability over time and place. There is a substantial scope for further research on choosing these redistribution proportions for each garbage code onto target underlying causes. Another important area for research will be to attempt to characterize the uncertainty in the redistribution algorithms, so that this uncertainty can be reflected in the adjusted death rates for a cause in a particular country and year.
Bobby Reiner, Simon Hay, Katie Welgan, Chris Troeger, Mathew Baumann, Brigette Blacker, Molly Miller-Petrie, Lucas Earl, Daniel Casey, Aubrey Cook, Farah Daoud, Nicole Weaver, Samath D. Dharmaratne, Laura Dwyer-Lindgren, Valery Feigin, Joseph Frostad, Kimberly Johnson, Alice Lazzar-Atwood, Kate LeGrand, Stephen Lim, Paulina Lindstedt, Laurie Marczak, Benjamin Mayala, Tomislav Mestrovic, Ali Mokdad, Jon Mosser, Christopher J.L. Murray, QuynhAnh Nguyen, David Pigott, Puja Rao, David Smith, Emma Spurlock