Deaths

Classification of deaths

Since 1 January 2000, deaths in Scotland have been coded in accordance with the Tenth Revision of the World Health Organisation's International Statistical Classification of Diseases and Related Health Problems (ICD10) (for further information see below under the heading "The use of International Classifications in 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 National Records for Scotland (NRS; formally, GROS) by Procurators Fiscal are also taken into account.  Background information about vital events in general, and deaths in particular, can be found on the NRS website.

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 here (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).

Automated coding

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

From January 2017, NRS implemented new software (IRIS) for coding cause of death, replacing the previous Mortality Medical Data System (MMDS) software. The Impact of the Implementation of IRIS Software for ICD-10 Cause of Death Coding on Mortality Statistics in Scotland (PDF 259 Kb) describes the impact of implementing this new software.

How causes of death are recorded on death certificates, links to examples of the Medical Certificates of the Cause of Death (MCCD), guidance which is given to doctors and the main changes to the coding of cause of death can be found here: https://www.nrscotland.gov.uk/statistics-and-data/statistics/statistics-by-theme/vital-events/deaths/deaths-background-information/death-certificates-and-coding-the-causes-of-death

The use of International Classifications in Scotland

The first 'International Classification of Causes of Death' was developed at the end of the nineteenth century. During the twentieth century periodic revisions, latterly co-ordinated by the World Health Organisation (WHO), have been produced almost every decade. The Second Revision was the first to be used in Scotland, in the Registrar General's Annual Report for 1911. The revisions used for the remainder of the twentieth century are summarised in the table below. This shows that the Ninth Revision (ICD9) was used for a rather longer period, 1979-1999, than any of the earlier revisions. Since 1 January 2000 NRS has been coding cause of death using the Tenth Revision (ICD10). The full title of the classification changed a number of times during the last century, the Tenth Revision being renamed as the 'International Statistical Classification of Diseases and Related Health Problems'.

The purpose of the ICD is to promote international comparability in the collection, classification, analysis and presentation of mortality and morbidity statistics. The periodic revisions help the classification to stay abreast of medical advances, both in terms of disease identification and aetiology, and changes in medical terminology.

ICD10

The latest revision (ICD10) was developed by WHO together with nine international collaborating centres for the classification of diseases. These nine centres are based on regional and language groupings.

ICD10 was published in three volumes by WHO in the early 1990s. It incorporated the most fundamental changes to the ICD for almost 50 years and was designed for use well into the 21st century. Despite WHO's recommended implementation date of 1993, its introduction for mortality coding has generally been relatively slow, though a few countries did start to use it in the mid-1990s. It was introduced in Scotland in 2000 and in England and Wales, and in Northern Ireland in 2001 for deaths using ICD10.

In many countries ICD10 was used for morbidity coding from an earlier date, in Scotland's case from 1996.

Although released in the early 1990s, WHO had review groups that considered possible changes on a case by case basis and advise on amendments to the classification on a more regular basis on roughly an annual basis.

WHO recently revised ICD to an Eleventh Revision (first issued June 2018). The implementation date for collecting and reporting data using this revision has not as yet been agreed and is likely to be several years before it can be adopted by Scotland (and other countries) for coding either morbidity or mortality records.