4727.0.55.002 - Australian Aboriginal and Torres Strait Islander Health Survey: Users' Guide, 2012-13  
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APPENDIX 4: CLASSIFICATION OF BMI FOR CHILDREN

The following table shows the cut-off points for the grouping of BMI scores for overweight and obesity, by sex, for exact years and half-years between two and 18 years.

BMI cut-off points for children

Height and weight data for children in the AATSIHS was collected for children aged two years and over. As age is only available for whole years in the AATSIHS, BMI calculations for children are based on the half-year cut-off points, as these are considered to provide an essentially unbiased estimate of prevalence. For example, a child who is recorded in the survey as being seven years old may have just turned seven, or may be shortly turning eight, so the half-year cut-off provides a mid-point across all seven year olds in the survey. This methodology assumes a fairly even spread of ages in years and months for each age group.

Cut-off points for each grouping for children are based on corresponding cut-off points for persons aged 18 years and over. For example, a score of 22.77 for a nine year old boy is equivalent to a score of 30 (obese) for an adult, and a score of 14.81 for a ten-and-a-half year old girl is equivalent to a score of 18.5 (Normal) for an adult.

The cut-off points for normal weight (18.5 in adults) are sourced from Cole et al, Body mass index cut offs to define thinness in children and adolescents: international survey, 2007. The cut-off points for overweight (equivalent to a BMI score of 25 for an adult) and obesity (equivalent to a BMI score of 30 for an adult) are the cut-off points for children and adolescents sourced from Cole et al, Establishing a standard definition for child overweight and obesity worldwide: international survey, 2000.

The following table contains cut-off points for BMI for children. The first column gives the age in years. The second column provides the cut-off for normal BMI. Children with BMI less than this point are classified as underweight. The third column provides the cut-off for overweight BMI. Children with a BMI less than this cut-off and greater than the normal cut-off are consider to be of normal weight. The fourth column provides the cut-off for obese BMI. Children with a BMI less than this cut-off and greater than the overweight cut-off are considered to be overweight, while children with a BMI greater than this cut-off are considered to be obese.

BODY MASS INDEX (BMI) CUT-OFF POINTS FOR CHILDREN AND ADOLESCENTS
Normal — below this point considered underweight
Overweight — above this point and below obese considered overweight
Obese — above this point considered obese
Age (in years)
Adult cut-off point 18.5
Adult cut-off point 25.00
Adult cut-off point 30.00
Boys
2
15.14
18.41
20.09
2.5
14.92
18.13
19.80
3
14.74
17.89
19.57
3.5
14.47
17.69
19.39
4
14.43
17.55
19.29
4.5
14.31
17.47
19.26
5
14.21
17.42
19.30
5.5
14.13
17.45
19.47
6
14.07
17.55
19.78
6.5
14.04
17.71
20.23
7
14.04
17.92
20.63
7.5
14.08
18.16
21.09
8
14.15
18.44
21.60
8.5
14.24
18.76
22.17
9
14.35
19.10
22.77
9.5
14.49
19.46
23.39
10
14.64
19.84
24.00
10.5
14.80
20.20
24.57
11
14.97
20.55
25.10
11.5
15.16
20.89
25.58
12
15.35
21.22
26.02
12.5
15.58
21.56
26.43
13
15.84
21.91
26.84
13.5
16.12
22.27
27.25
14
16.41
22.62
27.63
14.5
16.69
22.96
27.98
15
16.98
23.29
28.30
15.5
17.26
23.60
28.60
16
17.54
23.90
28.88
16.5
17.80
24.19
29.14
17
18.05
24.46
29.41
17.5
18.28
24.73
29.70
18
18.50
25.00
30.00
Girls
2
14.83
18.02
19.81
2.5
14.63
17.76
19.55
3
14.47
17.56
19.36
3.5
14.32
17.40
19.23
4
14.19
17.28
19.15
4.5
14.06
17.19
19.12
5
13.94
17.15
19.17
5.5
13.86
17.20
19.34
6
13.82
17.34
19.65
6.5
13.82
17.53
20.08
7
13.86
17.75
20.51
7.5
13.93
18.03
21.01
8
14.02
18.35
21.57
8.5
14.14
18.69
22.18
9
14.28
19.07
22.81
9.5
14.43
19.45
23.46
10
14.61
19.86
24.11
10.5
14.81
20.29
24.77
11
15.05
20.74
25.42
11.5
15.32
21.20
26.05
12
15.62
21.68
26.67
12.5
15.93
22.14
27.24
13
16.26
22.58
27.76
13.5
16.57
22.98
28.20
14
16.88
23.34
28.57
14.5
17.18
23.66
28.87
15
17.45
23.94
29.11
15.5
17.69
24.17
29.29
16
17.91
24.37
29.43
16.5
18.09
24.54
29.56
17
18.25
24.70
29.69
17.5
18.38
24.85
29.84
18
18.50
25.00
30.00