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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 survey collected information about:

• the health status of the population, including long-term medical conditions experienced and recent injuries
• use of health services such as consultations with health practitioners and visits to hospital and other actions people have recently taken for their health
• health related aspects of people's lifestyles, such as smoking, diet, exercise and alcohol consumption
• demographic and socioeconomic characteristics.

SCOPE OF THE SURVEY

4 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.

5 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.

7 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.

9 Dwellings were selected at random using a multistage 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.

10 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.

11 At the request of the relevant health authorities:

• the sample in the Northern Territory (NT) was reduced to a level such that NT records contribute appropriately to national estimates but cannot support reliable estimates for the NT. This was requested to enable a larger NT sample to be used in the General Social Survey conducted by the ABS in 2002.
• the sample in the Australian Capital Territory was increased by around 60% to improve the reliability of estimates.

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 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.

Estimation

16 Survey estimates of counts of persons are obtained by summing the weights of persons with the characteristic of interest. Estimates of non-person counts (e.g. days away from work) are obtained by multiplying the characteristic of interest with the weight of the reporting person and aggregating.

Standardisation

17 Data for some social conditions contained in this publication are shown as age standardised estimates or percentages. Many health characteristics are age-related and to enable comparisons across population groups (e.g. between those who are employed and those not in the labour force) 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

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

Sampling error

19 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 Note. 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

20 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.

21 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.

22 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 were 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.

• 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.

HEALTH PRODUCTS AND SERVICES

Microdata

26 For users who wish to undertake more detailed analysis of the survey data, a confidentialised unit record file (CURF) is available on CD-ROM. Other access to the confidentialised micro data includes an expanded CURF available via the NHS remote access data laboratory (RADL). Information about these confidentialised unit record files is contained in the publication Information Paper: National Health Survey - Confidentialised Unit Record Files (cat. no. 4324.0), which is available on the ABS web site .

Special tabulations

27 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 .

RELATED PUBLICATIONS

28 Other ABS publications which may be of interest are shown below. Most of these are available at .

• National Health Survey: Summary of Results, 1989-90, 1995 and 2001 (cat. no. 4364.0).
• National Health Survey: Users' Guide, 1989-90, 1995 and 2001 (cat. no. 4363.0).
• Mental Health and Wellbeing: Profile of Adults, Australia, 1997 (cat. no. 4326.0).
• Mental Health and Wellbeing: Users' Guide, 1997 (cat. no. 4327.0).