2. Data sources

2.1 The National Records of Scotland (NRS) - holds details of all deaths which are registered in Scotland. By convention, deaths are counted on the basis of the calendar year in which they are registered rather than the year of occurrence (as the latter might not be known). NRS closes its statistical database for a calendar year about five or six months after the end of the calendar year. The statistics for 2013 are based upon the information which NRS had obtained by mid-June 2014. NRS classifies the underlying cause of each death using International Statistical Classification of Diseases and Related Health Problems (ICD) codes, based on what appears in the medical certificate of the cause of death together with any additional information which is provided subsequently by (e.g.) certifying doctors, pathologists and Procurators Fiscal.

2.2 Drug-related deaths are identified using details from the death registrations supplemented by information from a specially-designed questionnaire, which is completed by forensic pathologists and lists the drugs and solvents that were found. NRS requests this information for all deaths involving drugs or persons known, or suspected, to be drug-dependent. Additionally, NRS follows up all cases of deaths of people where the information on the death certificate is vague or suggests that there might be a background of drug abuse. This enhancement to the data collection system was described in a paper published by NRS in June 1995 (which is referred to in Annex C). A copy of the questionnaire that was used from 2008 to 2013 is in Annex D (a new version was introduced at the start of 2014). In the case of deaths which involved drugs which are available on prescription, NRS does not know whether those drugs had been prescribed to the deceased: such information is not collected by the death registration process nor by the pathologists' questionnaires. Therefore, NRS does not know how many of the deaths which involved (say) methadone were of people who had been prescribed the drug (some information about this is available from the NHS reports referred to in paragraph B9 of Annex B).

2.3 The questionnaire was revised for 2008, in order to collect more complete information about the substances present in the body. This caused a break in the series of figures for 'drugs reported' because:

2.4 NRS's data from the questionnaires for 2008 onwards distinguish between (a) drugs which were implicated in, or which potentially contributed to, the cause of death and (b) any other drugs which were present, but which were not considered to have had any direct contribution to the death. As a result, NRS can produce figures for 2008 onwards:

Following consultation with the National Forum on Drug-related Deaths, 'drugs which were implicated in, or which potentially contributed to, the cause of death' became the standard basis for the figures for 2008 onwards that NRS produces for individual drugs, with effect from the 2009 edition.

2.5 It should be noted that, although the old questionnaire referred to the 'principal drug …' and 'other drugs … involved', the figures for 2007 and earlier years are not directly comparable to the figures for 2008 onwards on the new standard basis. This is because, in 2007 and earlier years, some pathologists reported, in the old questionnaire, all the drugs that they found (i.e. not just the drugs that they believed were implicated in, or contributed to, the cause of death) - so they provided information on the 'all drugs which were found to be present in the body' basis (i.e. not on the new standard basis). More information about the change (including why NRS cannot produce figures on the standard basis for 2007 or earlier years) is available in the 2009 edition.

2.6 At the start of 2011, NRS implemented a number of World Health Organisation (WHO) updates to the ICD rules for identifying the underlying cause of death. This caused a break in the series of figures for the underlying cause of death. 'Drug abuse' deaths from 'acute intoxication', which would previously have been counted under 'mental and behavioural disorders due to psychoactive substance use', are now counted under the appropriate 'poisoning' category. Examples are the deaths of known or suspected habitual drug abusers, for whom the cause of death was certified as 'adverse effects of heroin', 'methadone toxicity' or 'morphine intoxication'. Under the old coding rules, the underlying cause of those deaths would have been 'mental and behavioural disorders due to use of opioids' (unless NRS had been informed that the deaths were due to intentional self-harm, or assault, in which case the underlying cause would have been 'intentional self-poisoning …' or 'assault by drugs …', whichever was appropriate).

2.7 Under the new coding rules, the underlying cause of such deaths is the appropriate type of poisoning. For example, if NRS is informed that the overdose is believed to have been accidental, the underlying cause will be coded as 'accidental poisoning by and exposure to narcotics and psychodysleptics (hallucinogens)'. A note on the changes to the way in which NRS has coded the underlying cause of death with effect from the start of 2011 is available within the Death Certificates and Coding Cause of Death section of its website. NRS has estimated what the figures for 2011 onwards would have been, had the data been coded using the old rules. This makes it possible to see the changes between 2010 and 2011, and the longer-term trends, without a break in the series. NRS hopes to continue to estimate the breakdown by underlying cause of death on the basis of the old coding rules for at least a few more years.

2.8 The overall total number of drug-related deaths has not been affected by the changes to (i) the basis of the figures for individual drugs and (ii) how the underlying cause of death is coded. The first change has just reduced the number of drugs that are counted, for the purpose of the standard figures, for some deaths; the second has just altered the categories for the underlying cause of death against which many deaths are counted.

2.9 The statistics of drug-related deaths may be affected by other differences, between years and/or between areas, in the way in which the information was produced. For example: