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Table 1 Demographics of Western Australian (2000–2013) and New South Wales’ (2002–2008) births by plurality and Aboriginality

From: Pregnancy and birth characteristics of Aboriginal twins in two Australian states: a data linkage study

  Western Australia
(2000–2013)
New South Wales
(2002–2008)
Aboriginal Aboriginal Non-Aboriginal
Demographics Twin
N = 880
n (%)
Singleton
N = 33,229
n (%)
Twin
N = 794
n (%)
Singleton
N = 31,524
n (%)
Twin
N = 18,338
n (%)
Singleton
N = 582,355
n (%)
Groups compared and statistical significance reported1 A A B B C C
   D   D  
Maternal characteristics
 Age (mean (SD)) 26.6 (5.9) 24.9 (6.0) 27.5 (6.2) 25.7 (6.2) 31.5 (5.2) 30.1 (5.5)
 Age group ABCD
  < 20 112 (13) 6909 (21) 75 (9) 5616 (18) 268 (1) 17,969 (3)
  20–24 232 (26) 10,561 (32) 217 (27) 9537 (30) 1610 (9) 79,062 (14)
  25–29 282 (32) 8165 (25) 208 (26) 7662 (24) 4256 (23) 160,857 (28)
  30–34 156 (18) 5026 (15) 164 (21) 5609 (18) 6893 (38)2 198,560 (34)
  35+ 98 (11) 2560 (8) 130 (16) 3082 (10) 5307 (29)2 125,749 (22)
 Parity (mean (SD)) 1.9 (1.9) 1.7 (1.8) 1.8 (1.8) 1.5 (1.7) 0.9 (1.2) 1.0 (1.1)
 Parity group ABCD
  0 234 (27) 10,773 (32) 224 (28) 11,058 (35) 8120 (44) 244,868 (42)
  1 220 (25) 8352 (25) 206 (26) 8370 (27) 6003 (33)2 197,772 (34)
  2+ 426 (48) 14,104 (42) 364 (46) 12,024 (38) 4181 (23)2 138,629 (24)
 Previous multiple birthA 26 (3) 465 (1)
 Insurance at time of birtha 64 (7) 1621 (5)
 Socioeconomic disadvantageBCD
  Quintile 1 (most advantaged) 64 (7) 1946 (6) 56 (7) 1246 (4) 4489 (25) 125,066 (22)
  Quintile 2 82 (9) 3083 (9) 74 (9) 2877 (9) 3059 (17) 93,835 (16)
  Quintile 3 156 (18) 5249 (16) 166 (21) 5906 (19) 3639 (20)2 115,981 (20)
  Quintile 4 182 (21) 7612 (23) 278 (35) 12,240 (39) 4115 (23)2 138,903 (24)
  Quintile 5 (most disadvantaged) 390 (45) 14,778 (45) 214 (27) 8982 (29) 2884 (16) 103,054 (18)
 Remoteness of residenceabCD
  Major cities 394 (45) 14,004 (42) 386 (49) 14,410 (46) 14,702 (81) 456,767 (79)
  Inner regional 66 (8) 2131 (6) 256 (32) 10,052 (32) 2671 (15)2 91,304 (16)
  Outer regional 128 (15) 5272 (16) 120 (15) 5436 (17) 761 (4)2 26,874 (5)
  Remote 168 (19) 6187 (19) 20 (3) 1217 (4) 52 (< 1) 1806 (< 1)
  Very remote 124 (14) 5585 (17) 6 (1) 136 (< 1) 0 (0) 88 (< 1)
Infant characteristics
 SexC
  Male 450 (51) 16,823 (51) 404 (51) 16,169 (51) 9190 (50) 299,820 (51)
  Female 430 (49) 16,404 (49) 390 (49) 15,350 (49) 9146 (50) 282,499 (49)
Same sex twin3 648 (74) 546 (69) 12,252 (67)
  1. SD standard deviation. 1The superscripts ABCDabcd which appear next to the demographic factors indicate whether two groups were statistically significantly different: A or a for a comparison of WA Aboriginal singletons and twins; B or b for a comparison of NSW Aboriginal singletons and twins; C or c for a comparison of NSW non-Aboriginal singletons and twins; and D or d for a comparison of NSW Aboriginal twins and NSW non-Aboriginal twins. Pearson’s chi-squared tests were conducted for binary variables and Cochran-Armitage trend test for ordinal variables. A capital letter indicates p < 0.001 and a lower-case letter indicates 0.001 < p < 0.05. 2Some twin pairs had inconsistent information on their two birth records. 3Data were not available on zygosity. Data were missing for: maternal age (0 infants in WA, 180 infants in NSW), maternal parity (0 infants in WA, 1192 infants in NSW), insurance at time of birth (380 infants in WA), socioeconomic disadvantage (567 infants in WA, 5947 infants in NSW), remoteness of residence (50 infants in WA, 5947 infants in NSW), sex (2 infants in WA, 43 infants in NSW) and same sex twin (4 infants - 2 twin pairs - in WA)