BODY MASS AND PHYSICAL MEASUREMENTS
Definition
This topic refers to respondents' physical measurements and other self-perception questions including:
- the height (cm), weight (kg) and waist circumference (cm) of respondents as measured during the interview
- body mass index (BMI) derived from the height and weight physical measurements
- self-reported assessment of body mass.
In addition, the NHS collected information on perceived change in weight in the last 12 months and the NNPAS collected information on the respondent's satisfaction with their weight, and whether they were on a diet and if so what type.
Body Mass Index (BMI) or Quetelet's index is a useful tool, at a population level, for measuring trends in body weight and helping to define population groups who are at higher risk of developing long-term medical conditions associated with a high BMI, for example Type 2 diabetes and cardiovascular disease.
Waist circumference reflects mainly subcutaneous abdominal fat storage, and according to a
World Health Organisation (WHO) joint report has been shown to positively correlate to disease risk. The scale used for determining risky waist circumference is as recommended by the World Health Organisation, (See
Obesity: preventing and managing the global epidemic. Report of a WHO Consultation, 2000).
Population
Physical measurements were obtained for all persons, excluding pregnant women, aged 2 years and over in the NHS and NNPAS who agreed for the measurements to be taken.
Self-perceived body mass and other survey-specific questions were asked of all persons aged 15 years and over in the NHS and NNPAS.
Methodology
Information about physical measurements was collected in both the NHS and the NNPAS surveys. Information on physical measurements was first published in the
First Results publication based on the NHS only sample of approximately 19,700 people aged 2 years and over. Updated results on physical measures for the larger combined, core sample of approximately 32,000 people aged 2 years and over were published in the
Updated Results publication. For comparison of physical measurements with NHS only items, the NHS file should be used and similarly for comparison with NNPAS only items, the NNPAS file should be used. However, for the most accurate information for physical measurements alone or comparison with other items collected in the core, the core file should be used. For more information on the structure of the AHS, see the
Structure of the Australian Health Survey page of this Users' Guide.
Physical measurements
Physical measurements were taken towards the end of the survey. All physical measurements were voluntary, and women who had identified they were pregnant were not measured. Interviewers used digital scales to measure weight (maximum 150kg), a stadiometer to measure height (maximum 210cm), and a metal tape measure (which avoided the risk of the tape stretching) to measure waist circumference (maximum 200cm). Thorough interviewer training identified the points at which waists were to be measured as recommended by a World Health Organisation report, as well as how to take the measurements with the least amount of respondent discomfort. For waist measurements, interviewers held the end of the tape at the appropriate point and asked the respondent to turn around until the tape met, or asked the respondent to hold the end of the tape and walked around them until the tape met.
Interviewers encouraged respondents to remove their shoes and any heavy clothing, e.g. jumpers, before they took measurements, however, this was voluntary, and may not have occurred in some cases. Interviewers were not required to record if they thought clothing may have impacted significantly on measurements. Weight was recorded in kilos to one decimal point, and height and waist measurements were recorded in centimetres to one decimal point. Waist measurements were taken by placing the tape measure across the top of the belly button. If a respondent's waist measurement was more than two meters (the maximum measurement of the tape measure), interviewers were instructed to record this as 200.0cm. If a respondent's weight was self-reported to be more than 150 kilograms (the maximum measurement of the scales used) the weight was not recorded.
In order to validate the taken height and waist measurements, a random 10% of respondents were selected to be measured an additional time. If this second measurement of height or waist varied by more than one centimetre then a third reading was taken. Weight measurements were only taken once. For output purposes only the first measurement is used.
Body Mass Index
Body mass index (BMI) scores were derived using Quetelet's metric body mass index which is calculated as weight (kg) divided by height (m)2. BMI scores are commonly grouped for output. Whist the cut off points for different ethnic groups can vary, the World Health Organisation recommends that the same cut off points be used for international classification. The detailed output classifications available are shown in the table below. 2011-12 AHS publications use aggregated categories for estimates in published tables.
| Category | BMI score |
|
| Underweight |  |
| Class 3 | Less than 16 |
| Class 2 | 16.0 to less than 17.0 |
| Class 1 | 17.0 to less than 18.5 |
| Normal range | |
| Normal | Adult: 18.5 to less than 20.0; Child: 18.5 to less than 25.0(a) |
| Normal (Adult only) | 20.0 to less than 25.0 |
| Overweight | |
| | 25.0 to less than 30.0 |
| Obese | |
| Class 1 | Adult: 30.0 to less than 35.0; Child: 30.0 or more (a) |
| Class 2 (Adult only) | 35.0 to less than 40.0 |
| Class 3 (Adult only) | 40 or more |
|
(a) Child cut-offs identified in this table are in terms of Adult cut-offs. While the formula to calculate BMI scores is the same for adults and children, the classification of children's BMI is different to that of persons aged 18 years and over, and takes into account individual age and sex. BMI cut-off ranges for children 2 to 17 years of age are included in Appendix 4: Classification of BMI for children. Half-year cut-off points are used to calculate children's BMI scores for persons aged 2 to 17. Two versions of the data item are available, one using the mid-year cut-off and one using the whole-year cut-off.
Waist circumference
Waist circumference reflects mainly subcutaneous abdominal fat storage, and according to a
World Health Organisation (WHO) joint report has been shown to positively correlate to disease risk. The scale used for determining risky waist circumference is as recommended by the WHO, (See
Obesity: preventing and managing the global epidemic. Report of a WHO Consultation, 2000). As with BMI, the cut-off points in this scale are best used for people of European origin. However, as ethnicity cannot be determined, the same cut-off points are used for all respondents.
| Waist circumference guidelines, Adults |
|
| Not at risk | Increased risk | Substantially increased risk |
|
| Males | Less than 94 cm | 94 cm or more | 102 cm or more |
| Females | Less than 80 cm | 80 cm or more | 88 cm or more |
|
Self-perception questions
Respondents were asked whether they considered themselves to be:
- acceptable weight
- underweight
- overweight.
This question was not asked where:
- a female had previously identified themselves as currently pregnant (or raised it at this point)
- a proxy was being used for a respondents aged 15-17 years
- where a proxy was being used for an adult interview and the respondent was not present
NHS respondents (excluding females identified as currently pregnant) were asked whether, since this time last year, their weight had:
- increased
- decreased
- stayed the same.
NNPAS respondents were also asked whether they were on any kind of diet to lose weight or for some other health related reason. If they answered yes to being on a diet they were asked about the kind of diet(s) they were on:
- weight loss or low calorie diet
- low fat or cholesterol diet
- low salt or sodium diet
- sugar free or low sugar diet
- low fibre diet
- high fibre diet
- diabetic diet
- low carbohydrate diet
- high protein diet
- weight gain diet
- other.
Some examples of ‘other’ diets include: Low GI, high carbohydrate, low protein and medical restrictions on specific foods.
NNPAS respondents were then also asked how satisfied they were with their current weight:
- very satisfied
- satisfied
- neither satisfied nor dissatisfied
- dissatisfied
- very dissatisfied.
Data items
The data items and related output categories for this topic are available in Excel spreadsheet format from the
Downloads page of this product.
Interpretation
Points to be considered when interpreting data for this topic include the following.
- BMI was only calculated for persons for whom height and weight were measured. For 2011-12, 82.8% of respondents aged 2 years and over had their height and weight measured. This comprises 79.9% of children aged 2-17 who had their height and weight measured, and 83.6% of respondents 18 years and over who had their height and weight measured. The results presented as part of the AHS relate to the measured population only. Analysis of the characteristics of people who agreed to be measured compared to those who declined indicated that age and sex were factors in non-response. Females were more likely to decline, and non-response increased with age.
- While BMI is a useful tool to assess and monitor changes in body mass at the population level, it may be an inappropriate measure of the body fatness of certain populations and certain individuals; for example, those whose high body mass is due to muscle rather than fat, those with osteoporosis who have lower than usual BMI, or those of non-European background, whose risk levels are not accurately reflected in the BMI cut-off points used. BMI can, however, be used in conjunction with waist circumference which provides a second indicator for people at risk.
- For the most part, body mass questions were not asked where a proxy was responding on behalf of the respondent. However, where items have been asked of a proxy some care should be used.
- The NNPAS questions on current diet are based on self-report diet information. Respondents may not be aware of the purpose of their diet when for medical reasons, and one diet may be reported under multiple diet types.
Comparability with 2007-08
Data collected on measured height, weight and waist circumference in the 2011-12 surveys used the same methodology as the 2007-08 NHS survey and is therefore directly comparable. Differences in the equipment used for measurements are not expected to impact comparability.
However when making comparisons it should be noted that the 2011-12 surveys collected measurements from persons aged 2 years and over, whereas in the 2007-08 NHS, measurements were collected from persons aged 5 years and over. Care should be taken to ensure that the correct population has been selected when making comparisons. It should also be noted that in 2011-12, 83.1% of respondents aged 5 years and over had both their height and weight measured compared to 69.1% in 2007-08.
The 2011-12 surveys did not collect self-reported height and weight. Hip measurements were also not collected in 2011-12.
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