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Definition and purpose of classifications
The ISO standard 17115 defines a classification as ‘an exhaustive set of mutually exclusive categories to aggregate data at a pre-prescribed level of specialization for a specific purpose’. Classification involves the categorization of relevant concepts for the purposes of systematic recording or analysis.'
‘Classifications are used to support statistical data across the health system. To this end WHO has developed two reference classifications that can be used to describe the health state of a person at a particular point in time. Diseases and other related health problems, such as symptoms and injury, are classified in the International Classification of Diseases, now in its 10th revision (ICD-10). The second Classification is related to limitations in daily life: International Classification of Functioning, Disability and Health (ICF).'
‘This Family of International Classifications that has been endorsed by the WHO to describe various aspects of the health and the health system in a consistent manner. The purpose of the Family is to assist the development of reliable statistical systems at local, national and international levels, with the aim of improving health status and health care.’
‘Internationally endorsed classifications facilitate the storage, the retrieval, analysis, and interpretation of data and their comparison within populations over time and between populations at the same point in time as well as the compilation of internationally consistent data.’
The International Classification of Diseases (ICD) is an international standard diagnostic classification for general epidemiological purposes. It is used to classify diseases and other health problems recorded on many types of health and vital records including death certificates and health records.
The ICD has already a long history. Over the years it has been revised periodically to incorporate changes in the medical field. ICD-10 is the latest in a series which has its origins in the 1850s. The first edition, known as the International List of Causes of Death, was adopted by the International Statistical Institute in 1893. The WHO took over the responsibility for the ICD at its creation in 1948.
The WHO continuously improves and actualizes the ICD-10. The WHO publishes annually a list of recent updates.
ICD-9 versus ICD-10
ICD-9 has been in use since 1979. ICD-10 is the long awaited diagnosis code revision, because ICD-9 was running out of codes. Hundreds of new diagnosis codes are submitted annually. ICD-10 allowed not only for more codes but also for greater specificity and thus better epidemiological tracking.
ICD-10 differs from ICD-9 in several ways although the overall content is similar: ICD-10 has alphanumeric categories rather than numeric categories in ICD-9, some chapters have been rearranged, some titles have been changes, conditions have been regrouped, ICD-10 has almost twice as many categories as ICD-9 and some fairly minor changes have been made in the coding rules for mortality.
Until 1997 the causes of death were coded in Belgium according to ICD-9. Since 1998, at the same time as the introduction of the new death certificate, Belgium uses ICD-10 for reporting mortality statistics.
Consequences of the transition from ICD9 to ICD10
The process using ICD-10 instead of ICD-9 affects many aspects of the mortality data system including extensive coder training, but also revision of the software program and analysis.
Coding is a complicated operation which needs a medical background and a profound knowledge of the classification and the accompanying international rules and practices. Therefore it is necessary to educate the coders especially for this work. Their work determines the quality of the data.
But not only coders need to be trained in this domain. Training is also very useful for the productivity of physicians and code users.
Adding the year 1998 (and later) to the previous years (1987-1997) in SPMA also required changes and adaptations of the software and analysis programs, because all the codes are alpha-numeric in ICD-10 instead of numeric in ICD-9.
Some differences between these two classifications can result in a trend break between 1997 and 1998 for some causes of death.
Conversion table for trend analysis
Because of the differences between ICD-9 and ICD-10, the WHO has never taken the risk to make a conversion from one classification to another. So an international standard conversion table showing for each specific cause/disease the corresponding code in ICD-9 and ICD-10 does not exist.
To make trend analysis still possible, the Scientific Institute of Public Health, Unit of Epidemiology, developed a conversion table. This conversion table is based on the work performed in other organisations (Flemish Community, Central Office for Statistics (CBS) of the Netherlands, Eurostat, CDC in USA) who also searched for solutions.
Such a conversion table has been applied in SPMA for the item "evolution over time of the specific cause mortality (predefined list)".