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Overview of key data sources: Deaths

Classification of deaths

Since 1 January 2000, deaths in Scotland have been coded in accordance with the Tenth Revision of the World Health Organisations International Statistical Classification of Diseases and Related Health Problems (ICD10) (see Uses of International Classifications on Scotland). The choice of underlying cause of death follows rules set out by WHO and is based on information collected on the medical certificate of cause of death together with any additional information provided subsequently by the certifying doctor. Changes notified to GROS by Procurators Fiscal are also taken into account, as is additional information about suicides supplied by the Crown Office.


Choosing the 'underlying' cause of death

Traditionally, tabulations of mortality statistics have presented information based on a single cause for each death and the early international classifications were devised to categorise the single cause normally reported on death certificates. However, as doctors began to report more than one condition on certificates, it became necessary to develop rules to select a principal or 'underlying' cause.

In the ICD the underlying cause is defined as

  • the disease or injury which initiated the train of morbid events leading directly to death, or
  • the circumstances of the accident or violence which produced the fatal injury.

For over 50 years WHO has recommended a specific format for collecting information on medical certificates of cause of death. The key part of the current Scottish form (Form 11) may be seen by clicking herePDF Button (9KB). This conforms to the latest format recommended by WHO in that it includes a fourth line in Part I where the sequence of causes directly leading to death is listed. In a correctly completed certificate the underlying cause should appear on the last completed line of Part I. The doctor may record other unrelated but contributing causes in Part II of the form.

If the certificate has not been completed properly, for example if the reported sequence of causes is illogical, it is necessary to have rules that, whenever possible, ensure the selection of an appropriate underlying cause of death. These selection rules are an integral part of the ICD.

There are also a number of modification rules which apply to particular conditions, combinations or circumstances, even when the certificate has been completed properly. For example, two or more mentioned conditions may be linked to derive a composite underlying cause, or a trivial condition unlikely to cause death may be rejected in favour of a more serious condition.


Bridge-coding exercise

Changes to the classification, and changes to the selection and modification rules described above, can have significant effects on the underlying causes chosen. When ICD10 was introduced in 2000, GROS carried out a bridge-coding or comparability study involving the  coding of a large sample of deaths using both the old (ICD9) and the new (ICD10) classifications. This enabled a detailed study of the discontinuities arising from changes to the classification and its associated rules. Such an understanding is crucial to the interpretation of mortality trends. Full details of this bridge coding study, which covered all deaths registered in 1999, can be found in Registrar General's 2000 Annual Report (see Appendix 2; 9.34 MB) PDF Button.


Automated coding

Over 30 years ago the National Center for Health Statistics (NCHS) in the United States began to develop software that would assign ICD codes to the causes reported on death certificates and consistently apply the complex coding rules set out in the ICD for choosing the underlying cause. The system uses a set of detailed decision tables developed by coding, classification and medical experts. Although automated coding works well, trained coders are still required to check and edit the input data and to resolve uncertainties and ambiguities.

The suite of programs developed by NCHS is now used by an increasing number of countries around the world including Scotland, where it was introduced (for ICD9 coding) in 1996. A short report on the introduction of automated coding appeared in Appendix 2 of the Registrar General's 1996 Annual Report.  An ICD10 version of the software has been used since 2000. The introduction of automated coding has been an important step in the direction of greater accuracy, consistency and international comparability.