CHANGES IN AGE AND SEX STRUCTURE

INTRODUCTION

This chapter presents information about changes in the counts of Aboriginal and Torres Strait Islander people between 2006 and 2011 by age and sex and by sex ratios (number of males per 100 females).


SUMMARY OF FINDINGS

• Nationally, for both Aboriginal and Torres Strait Islander males and females, large increases in Census counts were observed for all five-year age groups less than 65 years in 2011, with the exception of those aged 20-24 years.
• The pattern of increase by age group in the states and territories generally followed the national trend, with the exception of the Northern Territory which showed a decrease in counts of Aboriginal and Torres Strait Islander people in most age groups.
• The sex ratios for Aboriginal and Torres Strait Islander people aged 20 years and over in 2011, and particularly for those aged 20-24 years and 25-29 years in 2011, were generally lower than the trend for the total population.

AGE COHORTS

An age cohort is a group of people with the same birth year within a defined period (for example, people aged 30-34 years in 2011 who were aged 25-29 years in 2006). Age cohorts are used to look at a chosen group of people at points in time to assess whether changes to the group are in line with expectations. In theory, each age cohort in a demographically closed population will show fewer and fewer people in each successive Census as the population ages. This means that the population counts for Aboriginal and Torres Strait Islander people in each age cohort in the 2011 Census, except for children aged 0-4 years, should be lower than in the 2006 Census. For example, the 2011 Census count of people aged 30-34 years should be less than the count of those aged 25-29 years in 2006, and this count should be less than the count of those aged 20-24 years in 2001.

An age cohort which has more Aboriginal and Torres Strait Islander people in the 2011 Census than the 2006 Census can indicate an undercount for that cohort in the 2006 Census and/or more people entering into that age cohort in 2011. This can occur through migration, which generally does not apply to the Aboriginal and Torres Strait Islander population at the national level. For more information on migration, refer to the chapter Measuring Changes in Population between Censuses. It can also occur through other means, such as improved Census coverage and/or people identifying as an Aboriginal or Torres Strait Islander person in 2011 but not in 2006.

In 2011, there were more Aboriginal and Torres Strait Islander people counted in almost every five-year age cohort under the age of 65 years than in 2006. Aboriginal and Torres Strait Islander males and females aged 20-24 years in 2011 were the only age cohorts in this range to record a decrease in counts.



Of the 93,300 increase in Aboriginal and Torres Strait Islander people counted in the 2011 Census, most (72% or 67,400) were aged 0-4 years. The next largest proportional increases were for Aboriginal and Torres Strait Islander boys and girls aged 5-9 years (17% or 4,900 for boys and 16% or 4,400 for girls) and 10-14 years (11% or 3,300 for boys and 12% or 3,400 for girls) in 2011. Large increases were also observed for Aboriginal and Torres Strait Islander males in age groups from 30-54 years (5,200 or 8%) and females in age groups from 25-54 years (7,100 or 8%) in 2011.

Age cohorts by states and territories

In each of the states and territories, the increase in the Census counts of Aboriginal and Torres Strait Islander people by age group generally followed the national trend. Children and youth aged 0-14 years in 2011 accounted for the majority of the increase in the counts of Aboriginal and Torres Strait Islander people in 2011 in all states and territories.

Of Aboriginal and Torres Strait Islander people aged five years and over in 2011, the highest increases in counts across most of the states and territories were for children and youth aged 5-14 years in 2011 (that is, children aged 0-9 years in 2006). The Northern Territory showed an increase in the count of Aboriginal and Torres Strait Islander children aged 5-9 years in 2011, with a decrease in 10-14 year olds. Counts for Aboriginal and Torres Strait Islander people aged 60 years and over were lower than 2006 for all states and territories, which was in line with mortality expectations.

Most states and territories showed a decline in the counts of Aboriginal and Torres Strait Islander people aged 20-24 years in 2011, except for Victoria and the Australian Capital Territory which registered small percentage increases (2% and 11% respectively). As young adults are increasingly mobile, the increases in counts in Victoria and the Australian Capital Territory could reflect interstate mobility in part due to employment or higher education opportunities.

Among Aboriginal and Torres Strait Islander people aged 15 years and over in 2011, the highest percentage increases between the 2006 and 2011 Censuses were for those in age groups from 30-49 years. These increases occurred across all states and territories. This indicates the possibility of an undercount of people in these age cohorts in the 2006 Census or an increase in the number of people who identified as an Aboriginal and/or Torres Strait Islander person in the 2011 Census.

New South Wales

New South Wales recorded the largest count of Aboriginal and Torres Strait Islander people in 2011 and also recorded the largest increase in the count of Aboriginal and Torres Strait Islander people between 2006 and 2011. This increase was largely accounted for by children and youth aged 0-14 years in 2011 (81% or 27,700 of the total increase). Among Aboriginal and Torres Strait Islander people aged 15 years and over in 2011, those in the age groups from 35-54 years in 2011 accounted for the highest proportion of the overall increase in New South Wales (14% or 4,700).




Victoria

Between 2006 and 2011, there were consistent increases in the counts of Aboriginal and Torres Strait Islander people in Victoria in all five-year age groups up to 65 years and over, including those aged 20-24 years in 2011 (2% or 150). Aboriginal and Torres Strait Islander people aged 15 years and over in 2011 accounted for a larger proportion of the total increase in Victoria (24% or 1,800) than in the other states and territories. This could reflect an undercount in the 2006 Census or a higher propensity among people in these age groups to identify as an Aboriginal and/or Torres Strait Islander person in the 2011 Census. In particular, Aboriginal and Torres Strait Islander people in age groups from 30-49 years together contributed 14% (1,100) of the overall increase in Victoria.




Queensland

Queensland recorded the second largest count of Aboriginal and Torres Strait Islander people in 2011, after New South Wales, and also recorded the second highest increase in the counts of Aboriginal and Torres Strait Islander people between 2006 and 2011. The largest contributors to the total increase were children and youth aged 0-14 years in 2011 (90% or 25,400). Among Aboriginal and Torres Strait Islander people aged 15 years and over in 2011, small increases were observed for all age groups, apart from those aged 20-24 years and 65 years and over. In particular, Aboriginal and Torres Strait Islander people aged 30-34 years and 35-39 years in 2011 both accounted for 3% (800) of the overall increase.




South Australia

Children and youth aged 0-14 years in 2011 accounted for the majority of the total increase (90% or 4,400) in the counts of Aboriginal and Torres Strait Islander people in South Australia between 2006 and 2011. Among Aboriginal and Torres Strait Islander people aged 15 years and over in 2011, those aged 25-29 years and 40-44 years accounted for the highest proportions of the overall increase (3% or 140 each).




Western Australia

Western Australia followed the national pattern of change in Census counts of Aboriginal and Torres Strait Islander people in 2011, with the majority of the total increase contributed by children and youth aged 0-14 years in 2011. Among Aboriginal and Torres Strait Islander people aged 15 years and over in 2011, small increases were observed for all age groups, apart from those aged 20-24 years and 55 years and over. Aboriginal and Torres Strait Islander people aged 25-44 years in 2011 together accounted for the largest share of the overall increase in Western Australia (12% or 1,300).




Tasmania

Tasmania recorded one of the smallest counts of Aboriginal and Torres Strait Islander people in both 2006 and 2011. For this reason, percentage increases or decreases in each five-year age group could magnify small changes in the actual counts between the 2006 and 2011 Censuses.

In line with the national trend, Aboriginal and Torres Strait Islander children aged 0-4 years in 2011 accounted for the majority (84% or 2,400) of the total increase in the count of Aboriginal and Torres Strait Islander people in Tasmania between 2006 and 2011. Notably, among Aboriginal and Torres Strait Islander people aged 15 years and over in 2011, those in age groups from 35-49 years together accounted for a further 9% (250) of the overall increase. Like the Northern Territory, Tasmania also showed a decrease in the count of Aboriginal and Torres Strait Islander people aged 15-19 years in 2011 (down 3% or 80).




Northern Territory

The Northern Territory was the only jurisdiction in which there were consistent decreases between 2006 and 2011 in the Census counts for Aboriginal and Torres Strait Islander people in all five-year age groups from 10 years and over in 2011. Aboriginal and Torres Strait Islander children aged 0-9 years in 2011 accounted for the entire increase in the count of Aboriginal and Torres Strait Islander people in the Northern Territory.

Notably, as discussed in the chapter Measuring Changes in Population between Censuses, the Northern Territory experienced a net decrease of 26% (790) due to interstate mobility, the highest proportion of change of all the states and territories. While the counts presented here have not been adjusted for mobility, this suggests that mobility was likely to be a contributing factor to the decreases in counts for most age groups between 2006 and 2011.




Australian Capital Territory

Due to the small count of Aboriginal and Torres Strait Islander people in the Australian Capital Territory, the increase in the counts of Aboriginal and Torres Strait Islander people aged 15 years and over between 2006 and 2011 was very small for most five-year age groups. Aboriginal and Torres Strait Islander people in age groups under 35 years in 2011 accounted for 91% (1,200) of the total increase. Notably, Aboriginal and Torres Strait Islander people aged 20-34 years accounted for nearly one-quarter (24% or 310) of the overall increase between 2006 and 2011.




SEX RATIOS

A sex ratio provides the number of males per 100 females in a population or sub-population. Generally speaking, at birth the expected sex ratio for the total Australian population is approximately 105 males per 100 females (or 105.0). This rate usually declines to a point of parity (100 males per 100 females) for people aged 30-64 years, due to higher mortality rates at younger ages for males than for females. For those aged 65 years and over, the sex ratio usually reduces rapidly to less than 100 males per 100 females, again due to the impact of higher male mortality in these age groups.

Census counts of Aboriginal and Torres Strait Islander people aged 20-24 years in 2011 exhibited a much lower than expected sex ratio (99.9) when compared with the same age cohort five years earlier (105.4). A similar decrease was also apparent for Aboriginal and Torres Strait Islander people aged 25-29 years in 2011 (94.7 in 2011 compared with 99.1 in 2006). While this could be a result of a higher mortality rate for Aboriginal and Torres Strait Islander males than females in these age groups, it also suggests that fewer than expected young males were counted in the 2011 Census and/or the count of young females was higher than expected. This could be due to changes in the propensity to identify as an Aboriginal and/or Torres Strait Islander person in the Census, or changes in the undercount of young males and females in these age groups. For more information on estimates of the net undercount in 2011, refer to Census of Population and Housing - Details of Undercount, 2011 (cat. no. 2940.0).

Aboriginal and Torres Strait Islander people counted in the age groups 30-34 years through to 60-64 years in 2011 also had lower than expected sex ratios when compared with national trends. However, the rates are similar to those in the 2006 Census, so may be more in line with expectations for Aboriginal and Torres Strait Islander mortality rates.

	2006	2011	Difference
Age in 2011 (years)	ratio	ratio	% points
0-4	. .	104.0	. .
5-9	103.4	104.5	1.1
10-14	104.5	103.8	-0.7
15-19	105.1	106.6	1.5
20-24	105.3	99.9	-5.4
25-29	99.1	94.7	-4.4
30-34	93.9	92.7	-1.2
35-39	91.0	91.0	0.0
40-44	87.4	86.2	-1.2
45-49	88.6	89.7	1.1
50-54	90.3	90.2	-0.1
55-59	91.8	91.1	-0.7
60-64	90.0	88.4	-1.6
65-69	89.0	87.5	-1.5
70-74	81.5	78.0	-3.5
75-79	76.1	73.6	-2.5
80-84	68.4	61.7	-6.7
85 and over	58.0	53.3	-4.7
Total	97.0	97.2	0.2
(a) Usual residence Census counts. Excludes overseas visitors. Includes Other Territories.
(b) Number of males per 100 females. (c) Figures for 2006 are for age groups five years younger than in 2011 (for example, 85 years and over in 2011 is 80 years and over in 2006). Note: Totals and components may not be consistent within and between tables due to introduced random error to protect confidentiality of Census respondents - see Census Dictionary, 2011 (cat. no. 2901.0).

CONCLUDING REMARKS

In 2011, there were more Aboriginal and Torres Strait Islander people counted in almost every five-year age cohort under the age of 65 years than in 2006. The majority (72% or 67,400) of the increase in the Census counts of Aboriginal and Torres Strait Islander people was contributed by children aged 0-4 years in 2011. There were also large increases in counts of children and youth aged 5-14 years in 2011, males aged 30-54 years in 2011 and females aged 25-54 years in 2011. One explanation for the increases among these age cohorts is that some Aboriginal and Torres Strait Islander parents identified themselves and their children as being of Aboriginal and/or Torres Strait Islander origin in the 2011 Census but not in the 2006 Census. This is discussed in more detail in the chapter, Changing Propensity to Identify as Being of Aboriginal and Torres Strait Islander Origin between Censuses.