Notes

Australian Bureau of Statistics (ABS) changes to mortality coding over the study period

The following information on mortality coding is sourced from the ABS. For further information, see the ABS Causes of Death report.

Substantial changes to ABS cause of death coding were undertaken in 2006, improving data quality by enabling the revision of cause of death for open coroner’s cases over time. Deaths that are referred to a coroner (including deaths due to suicide) can take time to be fully investigated. To account for this, all coroner-certified deaths registered after 1 January 2006 are subject to a revisions process. This allows cause of death for open coroner’s cases to be included at a later stage where the case is closed during the revision period. Cause of death data are deemed preliminary when first published, with revised and final versions of the data being historically published 12 and 24 months after initial processing. Prior to 2006, revisions did not take place and as such it is recognised by the ABS that suicide deaths may have been understated during this period (ABS 2017).

As well as the above changes, new coding guidelines were applied to deaths registered from 1 January 2007. The new guidelines improve data quality by enabling deaths to be coded as suicide by ABS mortality coders if evidence from police reports, toxicology reports, autopsy reports and coroners’ findings indicates the death was due to suicide. Previously, coding rules required a coroner to determine a death as due to suicide for it to be coded as suicide.

The combined result of both changes has been the more complete capture of suicide deaths, and a reduced number of deaths coded as ‘undetermined intent’, within Australian mortality data.

Detailed information on coding guidelines for intentional self-harm, and administrative and system changes that can have an impact on the mortality data set, can be found in Explanatory Notes 88–96 of Causes of deaths report (ABS 2017).

Changes to previously published suicide information

As well as the addition of a new year of cause of death data, there are three main reasons for changes to previously published suicide results, as described below.

Lag in cause of death information for the most recent year of data, where a death is registered in the following year

Analysis in this study is based on year of occurrence of death. The National Death Index (NDI) is the source of information on fact of death in this study. Fact of death information from the NDI is supplemented with cause of death information from the National Mortality Database (NMD). Results published in the report Incidence of suicide in Australian Defence Force personnel: detailed analysis 2001–2015 for deaths that occurred in 2015 were based on preliminary cause of death information from the NMD. This was the most recent version of cause of death information at the time of reporting.

Analysis of the NMD for all Australian deaths shows that around 5% of deaths are not registered until the next year. These deaths are not captured in cause of death information, until data for the next year become available. This means that while fact of death information was complete for 2015 at the time of publishing the Incidence of suicide in Australian Defence Force personnel: detailed analysis 2001–2015, cause of death information was missing for around 7.5% of the deaths included in the analysis at that time. Additional suicides that occurred in 2015 but that were not registered until 2016 have now been identified with the inclusion of preliminary 2016 cause of death information in the current results.

Cause of death data revisions (ABS)

Cause of death information for the 2018 National suicide monitoring of serving and ex-serving ADF personnel release is based on final cause of death information for the years 2001 to 2013. Revised data are used for 2014 and preliminary data for 2015 and 2016. Cause of death for a small number of records linked to the 2014 (revised), 2015 (preliminary) and 2016 (preliminary) cause of death data may change where a death is being investigated by a Coroner and more up to date information becomes available as a result of the ABS revisions process. This may have a small effect on the number of deaths attributed to suicide in these years, as some deaths currently coded as ‘undetermined intent’ could later be identified as ‘intentional self-harm’.

Improvements in information available to the study

Changes to previously published results may also occur as additional information becomes available to the study.

For example, changes affecting recording of deaths in jurisdictional systems (including administrative and system changes, certification practices, classification updates or coding rule changes) can impact on the data sets underlying this study. Data users should note the potential impact of these changes when making comparisons between reference periods. While such changes will not explain all differences between years, they are a factor that may influence the magnitude of any changes in suicide numbers as revisions are applied (ABS 2017)

Rates based on low numbers

Rates based on low numbers of events can fluctuate from year to year for reasons other than a true change in the underlying frequency of the event.

In this report, rates are not reported when there are fewer than 5 events, as rates produced using low numbers can be sensitive to small changes in counts of deaths over time.

Suicide rates

When reporting how often suicide occurs, suicide rates account for the size of the underlying population. Whilst this measure does not account for differences in the age structures of the populations being compared, rates can be validly compared over time, across groups and to the corresponding Australian population.

Here, rates report how often suicides occur in the three ADF service status groups, and Australia, expressed as a number per 100,000 people.

Standardised mortality ratios

The standardised mortality ratio (SMR) is a widely recognised measure used to account for differences in age structures when comparing death rates between populations. The SMR is used to control for the fact that the three ADF service status groups have a younger age profile than the Australian population, and rates of suicide vary by age in both the study populations and the Australian population. The SMRs control for these differences, enabling comparisons of suicide rates between the three service status groups and Australia without the confounding effect of differences in age.

The SMR is calculated as the observed number of events in the comparison population (suicide deaths) divided by the number of events that would be expected if the study population had the same age- and sex-specific rates as those observed in the comparison population.

If the age- and sex-specific rates are the same for both populations (i.e. Australian and the ADF population) the SMR will be 1.0. If the rates are higher in the ADF population the SMR will be greater than 1.0, while if the ADF population rates are lower than the Australian population the SMR will be less than 1.0.

Using confidence intervals to test for statistical significance

Statistical significance is a measure that indicates how likely the observed difference is due to chance alone.

In this study, 95% confidence intervals (CIs) are provided for each standardised mortality ratio (SMR) and suicide rates to indicate the level of uncertainty around these estimates. Estimates produced using low numbers can be sensitive to small changes in numbers of deaths over time and will therefore have wide CIs. 95% CIs are provided within this report as they may account for the variation in absolute numbers of suicide deaths over time (related to the small sample size).

Use of CIs is the simplest way to test for significant differences. For the purpose of this report, differences are deemed to be statistically significant if CIs do not overlap with each other (when comparing suicide rates) or 1.0 (in the case of an SMR).

Static images in this report

An earlier version of this report had interactive Tableau figures with selectable data series as Figures 1, 2 and 3. This version instead uses static images for Figures 1, 2, and 3, with all data series from the original interactive figures given in the Appendix.

Acronyms

(21 Sep 2018)

ADF

Australian Defence Force

CI

Confidence Interval

DSD

Defence Suicide Database

NDI

National Death Index

NMD

National Mortality Database

PMKeyS

Personnel Management Key Solution

SMR

Standardised Mortality Rate

Data sources

The sources used here are the:

  • National Mortality Database (NMD). Cause of Death Unit Record File data are provided to the AIHW by the Registries of Births, Deaths and Marriages and the National Coronial Information System (managed by the Victorian Department of Justice) and include cause of death coded by the Australian Bureau of Statistics (ABS). The data are maintained by the AIHW in the NMD.

    Analysis in this report is based on year of occurrence of death. Year of death is an underestimate for the last year of data (2016), as some deaths are not registered until later years. Historical analysis of the NMD shows that this lag in registration results in around 5% late registrations each year.

    At the time of analysis, the causes of death data were final for 2013, revised for 2014 and preliminary for 2015 and 2016. Cause of death for a small number of deaths occurring in 2014, 2015 and 2016 are subject to further revision by the Australian Bureau of Statistics (ABS) and may be revised in future years.
  • National Death Index (NDI). The NDI is managed by the AIHW and contains person-level records of all deaths in Australia since 1980 obtained from the Registrars of Births, Deaths and Marriage in each state and territory. Its use is confined to data linkage studies approved by the AIHW Ethics Committee for health and medical research. NDI records are supplemented with cause of death information from the NMD (AIHW 2018).
  • Personnel Management Key Solution (PMKeyS). PMKeyS is a Defence staff and payroll management system that contains information on all people with Australian Defence Force (ADF) service on or after 1 January 2001 (when the system was introduced). This database contains demographic and service information at a given point in time and is linked to the NDI to identify deaths, including suicides, in the three ADF service status groups.
  • Defence Suicide Database (DSD). The DSD is maintained by Defence and contains information on suspected and confirmed deaths due to suicide of personnel serving full time since 1 January 2000. Suspected and confirmed suicides are included in the database only on the advice of the ADF Investigative Service. Cases are confirmed by receipt of a coronial finding of suicide. This database is linked to the PMKeyS and NDI and records with a status of ‘confirmed’ are used to supplement cause of death information from the NDI for numbers of suicides only.

References

Data quality statement

National Death Index (NDI).
The data quality statements underpinning the AIHW National Mortality Database can be found in the following Australian Bureau of Statistics (ABS) publications: