3302.0.55.003 - Life Tables for Aboriginal and Torres Strait Islander Australians, 2015-2017  
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USE OF THE CDE STUDY TO DERIVE ABORIGINAL AND TORRES STRAIT ISLANDER DEATHS IDENTIFICATION RATES

The CDE study allows a direct comparison of Indigenous status recorded on the death registration and the Census data for what is highly likely to be the same individual, and enables estimation of the undercoverage of Aboriginal and Torres Strait Islander deaths in the death registration system.

Table 3.3 presents the outcomes of the CDE study for Aboriginal and Torres Strait Islander deaths in Australia. It provides a cross-classification of the linked death registrations and Census records by the Indigenous status and age groups recorded in the respective records. Similar tables for other states and territory (without an age breakdown) where there are sufficient deaths available are in data cube 4: Summary of Linked Deaths by Indigenous Status, Deaths Registrations and Census Identification, Selected States and Territory and Australia - 2016-2017 (cat. no. 3302.0.55.003).


3.3 SUMMARY OF LINKED DEATHS BY INDIGENOUS STATUS, Australia - 2016-2017

DEATH REGISTRATION CLASSIFICATION
Aboriginal and Torres Strait Islander
Non-Indigenous
Not stated
Total
Census classification
no.
no.
no.
no.

0-14 years
Aboriginal and Torres Strait Islander
27
8
1
36
Non-Indigenous
2
388
3
393
Not stated
0
6
0
6
Total
29
402
4
435
15-59 years
Aboriginal and Torres Strait Islander
774
228
6
1 008
Non-Indigenous
82
1 4511
139
14 732
Not stated
19
288
2
309
Total
875
15 027
147
16 049
60 years and over
Aboriginal and Torres Strait Islander
1 084
476
7
1 567
Non-Indigenous
285
135 047
611
135 943
Not stated
42
5 592
27
5 661
Total
1 411
141 115
645
143 171
All ages
Aboriginal and Torres Strait Islander
1 885
712
14
2 611
Non-Indigenous
369
149 946
753
151 068
Not stated
61
5 886
29
5 976
Total
2 315
156 544
796
159 655

The table highlights a number of features:
  • of the 2,611 linked records identified as Aboriginal and Torres Strait Islander on the Census file, only 1,885 (72%) were identified as Aboriginal and Torres Strait Islander in death registrations;
  • the 1,885 records identified as Aboriginal and Torres Strait Islander in both datasets represented 81% (that is 1,885 / 2,315 * 100) of linked deaths identified as Aboriginal and Torres Strait Islander in death registrations;
  • there is misidentification of Indigenous status between the Census and death registrations (for example, Aboriginal and Torres Strait Islander in death registrations but non-Indigenous in Census, and vice versa);
  • the overall Aboriginal and Torres Strait Islander deaths identification rate indicated by these statistics is 89% (that is, 2,315 / 2,611* 100).

The above suggests that while there appears to be misidentification of Indigenous status between the Census and death registrations, the overall identification rate in the death registrations collection is quite high at the national level (89%).

At the same time, it needs to be recognised that at the national level, about 29% of Aboriginal and Torres Strait Islander deaths as recorded on the death registration form could not be linked to a Census record. This would occur due to missing or inconsistent information in the fields being used for linking and also undercount of the Aboriginal and Torres Strait Islander population in the Census counts. Despite these issues, it is considered that the linked data provide reasonable estimates of the identification rate of Aboriginal and Torres Strait Islander deaths.

For the purpose of compiling Aboriginal and Torres Strait Islander life tables, the Aboriginal and Torres Strait Islander ERP used was derived from Census counts adjusted by results of the Post Enumeration Survey (PES). The PES provides an independent check on Census coverage and also identifies key demographic characteristics of the population that have been missed or overcounted in the Census. In compiling Aboriginal and Torres Strait Islander ERP, Indigenous status reported by the PES was considered more reliable than that recorded in the Census.

Therefore, to be consistent with Aboriginal and Torres Strait Islander ERP calculations, the number of deaths reported as Aboriginal and Torres Strait Islander in Census in the CDE linked data were adjusted to a PES basis. It should be noted that these adjustments were only in respect of misclassifications of Indigenous status in the linked file. No attempt was, or could be, made for undercount identified in the PES; this is reflected in the non-matched death registrations.

Thus, the Aboriginal and Torres Strait Islander deaths identification rate using the linked data was derived by:
      1. calculating the propensities, from PES, of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status (to align the Census Indigenous status with the PES Indigenous status);
      2. applying the propensities to counts from the CDE linked data to obtain the expected number of deaths in Census on a PES basis; and
      3. taking the ratio of the number of deaths reported as Aboriginal and Torres Strait Islander in death registrations to that reported in Census on a PES basis to calculate the Aboriginal and Torres Strait Islander deaths identification rate.

The following step by step example illustrates the calculation of the identification rate of Aboriginal and Torres Strait Islander deaths for Australia using the improved method that include age-specific identification rates when calculating the underidentification adjustment.


Step 1: Calculation of propensities from PES data given in table 3.4

The propensities are calculated for persons who matched to Census and responded as Aboriginal and Torres Strait Islander in the PES to the Census Indigenous status question. They were estimated by the three response classes for the Census Indigenous status question: Aboriginal and Torres Strait Islander, non-Indigenous and not stated.

3.4 INDIGENOUS STATUS AS REPORTED IN 2016 CENSUS AND 2016 POST ENUMERATION SURVEY(a), Australia

PES RESPONSE
Aboriginal and Torres Strait Islander
Non-Indigenous
Total
Census classification
no.
no.
no.

0-14 years
Aboriginal and Torres Strait Islander
1 713
105
1 818
Non-Indigenous
90
17 203
17 293
Not stated
10
166
176
Total
1 813
17 474
19 287
15-59 years
Aboriginal and Torres Strait Islander
3217
209
3 426
Non-Indigenous
140
53 729
53 869
Not stated
28
352
380
Total
3 385
54 290
57 675
60 years and over
Aboriginal and Torres Strait Islander
386
36
422
Non-Indigenous
40
19 166
19 206
Not stated
3
230
233
Total
429
19 432
19 861
All ages
Aboriginal and Torres Strait Islander
5 316
350
5 666
Non-Indigenous
270
90 098
90 368
Not stated
41
748
789
Total
5 627
91 196
96 823

(a) This tables uses unweighted data for illustrative purposes. Weighted PES data was used when determining the propensities for calculating life tables.


The following example will refer to data for the 0-14 years age group in table 3.4:
  • P(ATSI/ATSI) = propensity of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status is 'Aboriginal and Torres Strait Islander' is 1,713 / 1,818 = 0.9422
  • P(ATSI/NI) = propensity of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status is 'non-Indigenous' is 90 / 17,293 = 0.0052
  • P(ATSI/NS) = propensity of being Aboriginal and Torres Strait Islander in PES given Census Indigenous status is 'not stated' is 10 / 176 = 0.0568

The above propensities are based on the unweighted PES data. In calculating Aboriginal and Torres Strait Islander ERP, weighted PES information was used. Therefore, to be consistent with Aboriginal and Torres Strait Islander ERP calculations, the propensities were calculated using the weighted PES data. This gave, for 0-14 years age group, P(ATSI/ATSI) = 0.8999 P(ATSI/NI) = 0.0044 and P(ATSI/NS) = 0.0446

The Australia level propensities P(ATSI/NI) and P(ATSI/NS) calculated above are based on relatively small numbers of PES responses (90 and 10 respectively for the 0-14 years age group). These propensities calculated at the state/territory level, while not disaggregated by age, are still unreliable as they are based on considerably smaller numbers of PES responses. To overcome this problem, national level P(ATSI/NI) and P(ATSI/NS) are used for the states and territories (though without any disaggregation by age, as outlined under Calculation of adjustment factor for the states and territory).


Step 2: Estimation of expected number of deaths in Census in linked data given in table 3.3 using PES Aboriginal and Torres Strait Islander propensities

The expected number of deaths in the Census in CDE linked data file, for persons aged 0-14 years, using PES Aboriginal and Torres Strait Islander propensities is:
  • = 36 * P(ATSI/ATSI) + 393 * P(ATSI/NI) + 6 * P(ATSI/NS)
  • = 36 * 0.8999 + 393 * 0.0044 + 6 * 0.0446
  • = 34

where the numbers 36, 393 and 6 are Aboriginal and Torres Strait Islander, non-Indigenous and not stated deaths in Census for the 0-14 years age group (table 3.3).


Step 3: Calculation of identification rate of Aboriginal and Torres Strait Islander deaths, Australia

The estimate of the Aboriginal and Torres Strait Islander deaths identification rate is then calculated by taking the ratio of the number of deaths reported as Aboriginal and Torres Strait Islander in death registrations to the number of deaths expected to be recorded as Aboriginal and Torres Strait Islander in Census using the PES Aboriginal and Torres Strait Islander propensities:

= 29 / 34

= 0.84

where 29 is the Aboriginal and Torres Strait Islander deaths in death registrations for the 0-14 years age group (table 3.3).


Step 4: Calculation of adjustment factor, Australia

The adjustment factor is taken to be the reciprocal of the identification rate of Aboriginal and Torres Strait Islander deaths:

= 1 / 0.84

= 1.19

In the linked data, 29 records for the 0-14 years age group were reported as Aboriginal and Torres Strait Islander on the death registration form (table 3.3). Of deaths linked to the Census, 34 were recorded as Aboriginal and Torres Strait Islander, after adjustment for classifying Indigenous status in the way that PES does. This means that fewer deaths were identified as Aboriginal and Torres Strait Islander in death registrations than were expected in Census on a PES basis. Therefore, for the 0-14 age group, the number of Aboriginal and Torres Strait Islander deaths according to death registrations needed multiplying by an adjustment factor of 1 / 0.84 = 1.19 to be comparable to the Aboriginal and Torres Strait Islander deaths expected to be recorded as such in the Census on a PES basis.

Steps 1-4 were repeated to calculate identification rates for the 15-59 and 60+ age groups. Identification rates were 0.93 and 0.92 for the 15-59 and 60+ age groups respectively.



3.5 ABORIGINAL AND TORRES STRAIT ISLANDER IDENTIFICATION RATES(a), Headline Australia(b) - 2015-2017

0-14
15-59
60+
Total(c)

Identification Rate
0.84
0.93
0.92
0.92
Adjustment Factor(d)
1.19
1.07
1.09
1.08

(a) Identification rate and adjustment factor are calculated using unrounded data.
(b) These life expectancy estimates are calculated taking age-specific identification rates into account.
(c) Total included here as a summary comparison measure, since the rates were applied at the age group level.
(d) Calculated as the reciprocal of the identification rate.



Calculation of adjustment factor for the states and territory

The procedure described above was used to derive Aboriginal and Torres Strait Islander deaths identification rates at the Australia level only. Identification rates for states, territory, remoteness areas and Index of Relative Socio-Economic Disadvantage were calculated using a similar method but without using age-specific identification rates. This method is detailed fully in Chapter 3 of Experimental Life Tables for Aboriginal and Torres Strait Islander Australians 2005-2007 (cat. no. 3302.0.55.003).

Due to small numbers of Aboriginal and Torres Strait Islander deaths in Victoria, South Australia, Tasmania and the Australian Capital Territory, it was not feasible to derive separate reliable Aboriginal and Torres Strait Islander deaths identification rates for these jurisdictions. Therefore, a single Aboriginal and Torres Strait Islander deaths identification rate was derived by grouping these together.

There is considerable variation in the identification rates at the state/territory level (table 3.6). The estimate is less than 1.0 for New South Wales, Western Australia and Victoria/South Australia/Tasmania/Australian Capital Territory/OT combined, which indicates a level of under-identification of Aboriginal and Torres Strait Islander deaths in death registrations relative to the Census on a PES basis. In contrast, Queensland and the Northern Territory indicates a slight over-representation of Aboriginal and Torres Strait Islander deaths in death registrations relative to the Census for linked records; that is, persons who are identified as Aboriginal and Torres Strait Islander in the death registrations collection exceeded those who identified as Aboriginal and Torres Strait Islander in the Census on a PES basis. There is no clear reason as to why this might be the case, although there is evidence that some Aboriginal and Torres Strait Islander deaths have a state of usual residence on the death registration that is different to the Census.



3.6 ABORIGINAL AND TORRES STRAIT ISLANDER IDENTIFICATION RATES, State/territory and Australia - 2015-2017

Aboriginal and Torres Strait Islander deaths according to death registrations
Expected number of Aboriginal and Torres Strait Islander deaths(a)
Identification rate
Adjustment factor(b)
State/territory
no.
no.
no.
no.

NSW
689
1 004
0.69
1.46
Qld
654
637
1.03
0.97
WA
353
376
0.94
1.06
NT
277
266
1.04
0.96
Vic./SA/Tas./ACT/OT combined
342
619
0.55
1.81
Aust.(c)(d)
2 315
2 902
0.80
1.25

(a) In Census if weighted PES Aboriginal and Torres Strait Islander propensities are used.
(b) Calculated as the reciprocal of the identification rate.
(c) These life expectancy estimates are calculated without taking age-specific identification rates into account.
(d) Includes all states and territories.

Aboriginal and Torres Strait Islander deaths identification rates for 2015-2017 are similar to those for 2010-2012, with the exception of Queensland for which the identification rate substantially increased to 1.03 in 2015-2017 from 0.80 in 2010-2012. This increase in the identification rate was due to an increase in the number of deaths of Aboriginal and Torres Strait Islander people following the introduction of Medical Certificate of Cause of Death (MCCD) in Queensland in 2015. For more information see Chapter 2: Data Quality Issues for deaths data.

Using MCCD information only, Queensland identified an extra 163 Aboriginal and Torres Strait Islander deaths: 30, 40 and 93 deaths in 2015, 2016 and 2017 respectively. Of these, only 84 deaths were in-scope for linkage and 70 deaths were successfully linked to a corresponding Census record. The exclusion of 70 linked deaths reduced the identification rate to 0.96 from 1.03.

To produce life tables for the period 2015-2017, three-year average deaths, rather than three-year total deaths were used. Therefore, inclusion of 54 (=163 divided by 3) of the 163 deaths identified using MCCD only reduced life expectancy, but this was compensated by adjusting down the registered deaths by the identification rate of 1.03. On balance, including the MCCD only deaths produced exactly the same life expectancy for Aboriginal and Torres Strait Islander males and only 0.1 year higher life expectancy for females compared with those produced by excluding them.


3.7 ABORIGINAL AND TORRES STRAIT ISLANDER IDENTIFICATION RATES, Remoteness Areas - 2015-2017

Aboriginal and Torres Strait Islander deaths according to death registrations
Expected number of Aboriginal and Torres Strait Islander deaths(a)(e)
Identification rate
Adjustment factor(b)
Remoteness Area
no.
no.
no.
no.

Major Cities
732
973
0.75
1.33
Inner and Outer Regional
1 002
1308
0.77
1.30
Remote and Very Remote
581
609
0.95
1.05
Aust.(c)(d)
2 315
2 902
0.80
1.25

(a) In Census if weighted PES Aboriginal and Torres Strait Islander propensities are used.
(b) Calculated as the reciprocal of the identification rate.
(c)These life expectancy estimates are calculated without taking age-specific identification rates into account.
(d) Includes all states and territories.
(e) Includes records for which remoteness classification is missing.

There is quite considerable variation in the identification rates by remoteness (table 3.7). The estimates of 0.75 for Major Cities and 0.77 for Inner and Outer Regional areas combined indicates a high level of under-identification of Aboriginal and Torres Strait Islander deaths in death registrations. In contrast, the identification rate of 0.95 for Remote and Very Remote areas combined indicates a much lower level of under-identification.



3.8 ABORIGINAL AND TORRES STRAIT ISLANDER IDENTIFICATION RATES, Index of Relative Socio-Economic Disadvantage - 2015-2017

Aboriginal and Torres Strait Islander deaths according to death registrations
Expected number of Aboriginal and Torres Strait Islander deaths(a)
Identification rate
Adjustment factor(b)
no.
no.
no.
no.

Most disadvantaged 20%
1074
1219
0.88
1.14
Second most disadvantaged 20%
579
719
0.80
1.24
Middle 20%
378
500
0.76
1.32
Least disadvantaged 40%
264
439
0.60
1.66

(a) In Census if weighted PES Aboriginal and Torres Strait Islander propensities are used.
(b) Calculated as the reciprocal of the identification rate.


Sensitivity analysis

The following table is used to illustrate the impact on life expectancy at birth when the identification rate is 5% higher or lower than those included in table 3.6. The variation is largest for the Northern Territory and Western Australia for both males and females. Life expectancy varies from 65.9 to 67.3 for males and 69.2 to 70.5 for females in the Northern Territory, and from 66.2 to 67.6 for males and 71.2 to 72.4 for females in Western Australia.



3.9 Aboriginal and Torres Strait Islander Life Expectancy, Assumed Identification Rates - 2015-2017

State/territory
If death identification rate was 5% less
Estimated death identification rate
If death identification rate was 5% more

MALES

NSW
70.2
70.9
71.5
Qld
71.4
72.0
72.6
WA
66.2
66.9
67.6
NT
65.9
66.6
67.3
Aust.(a)(b)
69.3
70.0
70.6

FEMALES

NSW
75.4
75.9
76.4
Qld
75.9
76.4
76.9
WA
71.2
71.8
72.4
NT
69.2
69.9
70.5
Aust.(a)(b)
73.9
74.4
75.0

(a) These life expectancy estimates are calculated without taking age-specific identification rates into account.
(b) Includes all states and territories.


DISCUSSION

The use of the CDE Indigenous Mortality Study to assess the identification rate of Aboriginal and Torres Strait Islander deaths in death registration data has a number of benefits but at the same time it has limitations. First, the obvious and most substantial benefit is that it enables direct calculation of identification rates. That is, they are derived by directly comparing Indigenous status as reported according to death registrations and Census data for linked records, as opposed to indirect and modelled estimates.

Second, no assumptions were necessary to derive the identification rates from the CDE study, whereas a number of subjective judgements and assumptions were necessary to produce identification rates prior to the 2005-2007 period.

The limitations of the CDE Indigenous Mortality Study relate to three main factors. First, the derived Aboriginal and Torres Strait Islander deaths identification rates relate to a restricted time frame from 9 August 2016 to 28 September 2017. It is not possible to accurately judge the appropriateness or otherwise of the derived Aboriginal and Torres Strait Islander deaths identification rates for past or future periods.

Second, of the 3,246 Aboriginal and Torres Strait Islander death records eligible for linkage, 931 (28.7%) were not linked to a corresponding Census record.Of all the unlinked records, 23.3% were in New South Wales, 27.1% in Queensland, 19.2% in Western Australia and 17.2% in the Northern Territory. While not unexpected given the relatively high Census undercount for Aboriginal and Torres Strait Islander Australians, there may be features or characteristics of the unlinked records that are quite different to the linked records and therefore may introduce some bias to the results. Sensitivity analysis (see Appendix 1) indicates this is likely to be small.

It should be noted that all unlinked Aboriginal and Torres Strait Islander deaths are included in life tables calculations, but they are excluded from the calculation of identification rates and the resulting adjustment factor that are applied to the life tables. To produce life tables for Aboriginal and Torres Strait Islander Australians, information on the number of Aboriginal and Torres Strait Islander deaths and the Aboriginal and Torres Strait Islander population are required. Data quality issues are discussed in Chapter 2: Quality issues with Aboriginal and Torres Strait Islander deaths and population data.

The life tables in this release are based on the average number of Aboriginal and Torres Strait Islander deaths registered in 2015-2017 and final Aboriginal and Torres Strait Islander population estimates for 30 June 2016 based on the 2016 Census results. To account for underidentification of Aboriginal and Torres Strait Islander deaths in death registrations, the numbers of Aboriginal and Torres Strait Islander deaths were adjusted according to the adjustment factors derived from the Census Data Enhancement Aboriginal and Torres Strait Islander Mortality Study. This is described in Chapter 3: Data linkage to derive Aboriginal and Torres Strait Islander deaths identification rates. The adjusted numbers of Aboriginal and Torres Strait Islander deaths in 2015, 2016 and 2017 were divided by three to obtain the average annual number of Aboriginal and Torres Strait Islander deaths over the period 2015-2017, and in conjunction with 30 June 2016 Aboriginal and Torres Strait Islander population estimates (mid-point between the 2015-2017 reference period) were used to calculate age-specific death rates for the Aboriginal and Torres Strait Islander population.

Third, as stated above, the propensities of Aboriginal and Torres Strait Islander identification as reported in the 2016 Census and 2016 PES are calculated for persons who matched to Census and PES. While PES is a sample representing the whole population, the current methodology implicitly assumes that the propensities based on the Census-PES match will apply for the death registrations linked to the Census. Appendix 1: Confidence Intervals provides some indication of the sensitivity of the estimates of Aboriginal and Torres Strait Islander life expectancy at birth to assumptions made when calculating it.

A further assumption relates to the application of identification rates, which assumed uniformity by age and sex - except for the headline Australia estimate (which used three broad age groups).

In spite of these limitations, the CDE Indigenous Mortality Study clearly shows the need to adjust for underidentification in Aboriginal and Torres Strait Islander death registrations.