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INTRODUCTION

1 This publication presents results from the National Health Survey (NHS) which was conducted throughout Australia from February to November 2001. This is the fifth in the series of health surveys conducted by the ABS; previous surveys were conducted in 1977-78, 1983, 1989-90 and 1995.

2 The statistics presented in this publication refer to data obtained on selected risk factors only. Additional health risk factor topics included in the 2001 NHS were:

• breastfeeding
• sun protection
• childhood and adult immunisation
• supplementary women’s health topics, and
• contraception/protection.

4 A supplementary health survey of Aboriginal and Torres Strait Islander people was conducted in association with the 2001 NHS. Information about that survey, together with summary results were separately published in National Health Survey: Aboriginal and Torres Strait Islander Results, Australia, 2001 (cat. no. 4715.0).

SCOPE OF THE SURVEY

5 The NHS was conducted in a sample of 17,918 private dwellings across Australia. Both urban and rural areas in all states and territories were included, but sparsely settled areas of Australia were excluded. Non private dwellings such as hotels, motels, hostels, hospitals, nursing homes and short-stay caravan parks were not included in the survey.

6 Within each selected household, a random sub-sample of usual residents was selected for inclusion in the survey as follows:

• one adult (18 years of age and over)
• all children aged 0-6 years
• one child aged 7-17 years.

8 The following groups were excluded from the survey:

• certain diplomatic personnel of overseas governments, customarily excluded from the census and estimated resident population figures
• persons whose usual place of residence was outside Australia
• members of non-Australian defence forces (and their dependants) stationed in Australia
• visitors to private dwellings.

SAMPLE DESIGN

Sample size and selection

10 Dwellings were selected at random using a multi-stage area sample of private dwellings. The initial sample selected for the survey consisted of approximately 21,900 dwellings; this reduced to a sample of approximately 19,400 after sample loss (e.g. households selected in the survey which had no residents in scope for the survey, vacant or derelict buildings, buildings under construction). Of those remaining dwellings, around 92% were fully responding, yielding a total sample for the survey of 26,863 persons.

11 To take account of possible seasonal effects on health characteristics, the sample was spread throughout the 10 months enumeration period. Conduct of the survey was suspended during the six weeks from 28 July to 10 September during the 2001 Census of Population and Housing enumeration period.

WEIGHTING AND BENCHMARKING

Weighting

12 Weighting is the process of adjusting results from a sample survey to infer results for the total population. To do this, a 'weight' is allocated to each sample unit. The weight is a value which indicates how many population units are represented by the sample unit.

13 The first step in calculating weights for each person was to assign an initial weight, which was equal to the inverse of the probability of being selected in the survey. For example, if the probability of a person being selected in the survey was 1 in 600, then the person would have an initial weight of 600 (that is, they represent 600 others).

Benchmarking

14 The initial weights were calibrated to align with independent estimates of the population of interest, referred to as 'benchmarks', in designated categories of sex by age by area of usual residence categories. Weights calibrated against population benchmarks compensate for over or under-enumeration of particular categories of persons and ensure that the survey estimates conform to the independently estimated distribution of the population by age, sex and area of usual residence, rather than to the distribution within the sample itself.

15 The survey was benchmarked to the estimated population living in private dwellings in non-sparsely settled areas at 30 June 2001 based on results from the 2001 Census of Population and Housing. Hence the benchmarks relate only to persons living in private dwellings, and therefore do not (and are not intended to) match estimates of the total Australian resident population (which include persons living in non-private dwellings, such as hotels) obtained from other sources.

Standardisation

16 Much of the comparative data contained in this publication are shown as age standardised estimates or percentages. Many health characteristics are age-related and to enable comparisons over time or across population groups (e.g. between states) the age profile of the populations being compared needs to be considered. The age standardised percentages are those which would have prevailed should the actual population have the standard age composition. In this publication the standard population is the benchmark population; i.e. the population at 30 June 2001 based on the 2001 Census of Population and Housing, adjusted for the scope of the survey. It should be noted that minor discrepancies in totals may occur between standardised and non-standardised estimates or percentages, as a result of the standardisation process.

RELIABILITY OF ESTIMATES

17 The estimates provided in this publication are subject to sampling and non-sampling error.

Sampling error

18 Sampling error is the difference between the published estimates, derived from a sample of persons, and the value that would have been produced if all persons in scope of the survey had been included. For more information refer to the Technical Notes. In this publication, estimates with a relative standard error of 25% to 50% are preceded by an asterisk (e.g. *3.4) to indicate that the estimate should be used with caution. Estimates with a relative standard error over 50% are indicated by a double asterisk (e.g. **0.6) and should be considered unreliable for most purposes.

Non sampling error

19 Non-sampling error may occur in any data collection, whether it is based on a sample or a full count such as a census. Sources of non-sampling error include non-response, errors in reporting by respondents or recording of answers by interviewers, and errors in coding and processing data.

20 Non-response occurs when people cannot or will not cooperate, or cannot be contacted. Non-response can affect the reliability of results and can introduce a bias. The magnitude of any bias depends upon the rate of non-response and the extent of the difference between the characteristics of those people who responded to the survey and those who did not.

21 The following methods were adopted to reduce the level and impact of non-response:

• face-to-face interviews with respondents
• the use of interviewers who could speak languages other than English where necessary
• follow-up of respondents if there was initially no response
• weighting to population benchmarks to reduce non-response bias.

• information about medical conditions was not medically verified and most was not necessarily based on diagnosis by a medical practitioner. Conditions which have a greater effect on people's wellbeing or lifestyle, or those which were specifically mentioned in survey questions are expected in general to have been better reported than others
• results of previous surveys have shown a tendency for respondents to under-report alcohol consumption levels and their weight, but over-estimate their height.

• a classification based on the International Classification of Diseases, 10th revision (ICD-10)
• a classification based on the 2 plus edition of the International Classification of Primary Care (ICPC)
• a classification based on the International Classification of Diseases, 9th revision (ICD-9), which is similar to the classification of conditions used in the 1995 NHS, and has been retained to assist data users in comparing 2001 and 1995 results.
• In this publication, medical conditions data from the 2001 NHS are shown classified to the ICD-10-based classification, or variants of that classification.

RESULTS OF THE SURVEY

Comparability with previous National Health Surveys

25 This publication contains some results from the last two NHSs. Understanding the comparability of data from the 2001 NHS with data from these other surveys is crucial to the use of the data and interpretation of apparent changes in health characteristics over time. While the 2001 NHS is similar in many ways, particularly to the 1995 NHS, there are important differences in sample design and coverage, survey methodology and content, definitions and classifications between previous NHSs. These will effect the degree to which data are directly comparable between the surveys.

26 The main differences between the 1995 and 2001 NHSs which may effect comparability of data presented in this publication are shown below. In this publication, data from previous surveys are only shown where a reasonable level of comparability exists.

27 While the number of dwellings sampled was slightly smaller in 2001, sub-sampling of persons within households has meant the number of persons sampled in 2001 was about half that in 1995 (in which several states purchased additional sample). This has reduced the reliability of some estimates.

28 The sample for the 1995 survey included some non-private dwellings and covered sparsely settled areas. The 2001 NHS survey included private dwellings in urban and rural areas only. However, both the sparsely settled and special dwelling populations are quite small and hence their exclusion in 2001 is regarded as having minimal impact on comparability, particularly at the data levels shown in this publication.

29 All persons in sampled dwellings were included in the 1995 survey, and only records from fully responding households were retained on the data file. In contrast the 2001 survey sub-sampled persons within households (one adult, all children 0-6 years, one child 7-17 years). To the extent that some health characteristics may be clustered within households, the different sampling approaches may impact slightly on comparability between surveys.

30 The 2001 survey was effectively enumerated over about a ten-month period, compared with a 12-month period for the 1995 survey. The 2001 survey was not enumerated in December or January, nor during a six-week period mid-winter (coinciding with conduct of the 2001 Census of Population and Housing).

31 As a result of the points above, some care should be taken in interpreting apparent changes over time in the prevalence of certain long term conditions and other health characteristics. Some movements between 1995 and 2001 estimates can, at least in part, be attributed to conceptual, methodological and/or classification differences. However, there are some instances where the degree or nature of the change suggests other factors are contributing to the movements, including changes in community awareness or attitudes to certain conditions, changes in common terminology for conditions, improvements in the diagnosis of certain conditions, etc. The degree of change attributable to all these factors, relative to actual change in the prevalence of characteristics, cannot be determined from information collected in this survey.

32 Further information about comparability between surveys is contained in National Health Survey: Users' Guide, Australia, 2001 (cat. no. 4363.0.55.001) and the Occasional Paper: Long-term Health Conditions - A Guide To Time Series Comparability From The National Health Survey (cat. no. 4816.0.55.001). Both the User's Guide and the Occasional Paper are available through the ABS web site . In addition, the ABS can offer advice, if required, on the comparison of the 2001 survey results with those from the 1995 or earlier surveys.

HEALTH PRODUCTS AND SERVICES

Results for states and territories

33 Summary results from this survey compiled separately for each state and the Australian Capital Territory (ACT) are available in tabular form on the ABS web site or on request to ABS.

Microdata

34 Users wishing to undertake more detailed analysis of the survey data may apply for access to either the BASIC or EXPANDED NHS Confidentialised Unit Record Files (CURFs). All clients wishing to access the NHS CURFs should refer to the 'Access to ABS CURFs' section located on the ABS web site, and read the Responsible Access to ABS Confidentialised Unit Record Files (CURFs) Training Manual, and other relevant information, before downloading the Application and Undertaking to apply for access. Any queries relating to Conditions of Sale should be referred to curf.management@abs.gov.au.

Special tabulations ions

35 Special tabulations are available on request. Subject to confidentiality and sampling variability constraints, tabulations can be produced from the survey incorporating data items, populations and geographic areas selected to meet individual requirements. These can be provided in printed or electronic form. A list of data items available from the survey is available free of charge on the ABS web site . Further information about the survey and associated products is available from the National Information and Referral Service. Details are listed at the front of this publication.

RELATED PUBLICATIONS

36 Other ABS thematic publications and web-based papers which may be of interest are shown below. Most of these are available at :

Thematic publications
National Health Survey: Summary of Results, 1989-90, 1995 and 2001, cat. no. 4364.0
National Health Survey: Summary Results, Australian States and Territories, 1995 and 2001, cat. no. 4368.0
National Health Survey: Users' Guide, 1989-90, 1995 and 2001, cat. no. 4363.0
National Health Survey: Injuries, Australia, 2001, cat. no. 4384.0
National Health Survey: Private Health Insurance, Australia, 1995, cat. no. 4334. 0
National Health Survey: Diabetes, Australia, 1995, cat. no. 4371.0
National Health Survey: Cardiovascular and Related Conditions, Australia, 1995, cat. no. 4372.0
National Health Survey: Asthma and Other Respiratory Conditions, Australia, 1995, cat. no. 4373.0
National Health Survey: Injuries, Australia, 1995, cat. no. 4384.0
National Health Survey: SF36 Population Norms, Australia, 1995, cat. no. 4399.0
Mental Health and Wellbeing: Profile of Adults, Australia, 1997, cat. no. 4326.0
National Survey of Mental Health and Wellbeing of Adults: Users' Guide, 1997, cat. no. 4327.0
National Nutrition Survey: Selected Highlights, Australia, 1995, cat. no. 4802.0
National Nutrition Survey: Foods Eaten, Australia, 1995, cat. no. 4804.0
National Nutrition Survey: Nutrient Intakes and Physical Measurements, Australia, 1995, cat. no. 4805.0
National Nutrition Survey: Users' Guide, 1995, cat. no. 4801.0
Children's Health Screening, 1995, cat. no. 4337.0
Children's Immunisation Survey, Australia, 1995, cat. no. 4352.0
Disability, Ageing and Carers, Australia: Summary of Findings, 1998, cat. no. 4430.0
Web-based papers
National Health Survey: Private Health Insurance, Australia, cat. no. 4815.0.55.001
Breastfeeding in Australia, cat. no. 4810.0.55 .001
Occasional Paper: Vaccination Coverage in Australian Children - ABS Statistics and the Australian Childhood Immunisation Register (ACIR), cat. no. 4813.0.55.001
Occasional Paper: Measuring Dietary Habits in the 2001 National Health Survey, Australia, cat.no. 4814.0.55.001
National Health Survey: Private Health Insurance, Australia, cat. no. 4815.0.55.001
Occasional Paper: Long-term Health Conditions - A Guide to Time Series Comparability From The National Health Survey, Australia, cat. no. 4816.0.55.001
Information Paper: Use of the Kessler Psychological Distress Scale in ABS Health Surveys, Australia, cat. no. 4817.0.55.001