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3 The statistics presented in this publication are a selection of the information available. Some emphasis has been given in this publication to providing information on National Health Priority Areas.
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 will be separately published in National Health Survey 2001: Aboriginal and Torres Strait Islander Results, Australia (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:
7 Subsampling of respondents enabled more information to be collected from each respondent than would have been possible had all usual residents of selected dwellings been included in the survey.
8 The following groups were excluded from the survey:
9 Trained ABS interviewers conducted personal interviews with selected residents of sampled dwellings. One person aged 18 years and over in each dwelling was selected and interviewed about their own health characteristics. An adult resident, nominated by the household, was interviewed about all children aged 0-6 years and one selected child aged 7-17 years in the dwelling. Adult female respondents were invited to complete a small additional questionnaire covering supplementary women's health topics.
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 Census of Population and Housing enumeration period.
12 At the request of the relevant health authorities:
WEIGHTING, BENCHMARKING AND ESTIMATION
13 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.
14 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).
15 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.
16 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.
17 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.
18 Data for states and the ACT and most time series data contained in this publication are shown as age (and sex) 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
19 The estimates provided in this publication are subject to sampling and non-sampling error.
20 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.
21 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.
22 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.
23 The following methods were adopted to reduce the level and impact of non-response:
24 By careful design and testing of questionnaires, training of interviewers, asking respondents to refer to records where appropriate, and extensive editing and quality control procedures at all stages of data processing, other non-sampling error has been minimised. However, the information recorded in the survey is essentially 'as reported' by respondents, and hence may differ from information available from other sources, or collected using different methodology. In particular it should be noted that:
Long term medical conditions
25 All reported long term medical conditions were coded to a list of approximately 1,000 condition categories which was prepared for this survey. Information about medical conditions classified at this level of detail will not generally be available for output from the survey; however, they can be regrouped in various ways for output. Three standard output classifications developed by the ABS for this survey are available:
26 In this publication, medical conditions data from the 2001 NHS are shown classified to the ICD10-based classification, or variants of that classification. Data from the 1989-90 and 1995 surveys are classified to the ICD9: although different classifications are used, conditions selected for inclusion in the publication were generally those where classification differences would have minimal impact on comparability. However, classification differences do reduce direct comparability for the categories complete/partial hearing loss, rheumatism and heart disease.
27 Pharmaceutical medications reported by respondents as used for asthma, diabetes mellitus/high sugar levels, cardiovascular conditions or cancer were classified into generic types. The classification used was developed by the ABS for this survey, but is based on the WHO Anatomical Therapeutic Chemical (ATC) classification, and the framework (based on organ system and therapeutic drug class) underlying the listing of medications in the Australian Medicines Handbook.
28 Country of Birth was classified according to the Standard Australian Classification for Countries.
29 Languages spoken at home were classified according to the Australian Standard Classification of Languages.
30 In this publication, survey results are shown compiled for Australia, individual states and the ACT, and broad categories from the Australian Standard Geographical Classification (ASGC) Remoteness Area classification. Results compiled at other levels of the ASGC can be compiled on request.
RESULTS OF THE SURVEY
Comparability with previous National Health Surveys
31 Summary results of the last two NHSs were published in National Health Survey, Summary of Results, Australia, 1989-90 and 1995 (cat. no. 4364.0). A range of other publications was also released from each of these surveys; see paragraph 39.
32 This publication contains some results from the last two NHSs, the 1995 Children's Immunisation and Health Screening Survey and the 1997 Survey of Mental Health and Wellbeing of Adults. 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. These will effect the degree to which data are directly comparable between the surveys.
33 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.
34 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.
35 Further information about comparability between surveys will be contained in National Health Survey, Users' Guide, Australia, 2001 to be available through this site from December 2002. 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
36 Summary results from this survey compiled separately for each state and the ACT are available in tabular form on this site or on request to ABS.
37 For users who wish to undertake more detailed analysis of the survey data, it is expected that a confidentialised unit record file will be available on CDROM towards the end of 2002. Arrangements for other access to confidentialised microdata are also being developed and are expected to be in place by the end of 2002. Those wishing to access such microdata should contact the Director, Health Section of the ABS.
38 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 this site. Further information about the survey and associated products is available from the contact officer listed at the front of this publication.
39 Other ABS publications which may be of interest are shown below. Most of these are available on this site:
National Health Survey, Summary of Results, Australia, 1989-90 and 1995, cat. no. 4364.0
National Health Survey, Summary Results, Australian States and Territories, 1995, cat. no. 4368.0
National Health Survey, Users' Guide, 1989-90 and 1995, cat. no. 4363.0
National Health Survey, Private Health Insurance, 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
Mental Health and Wellbeing: 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, Australia, 1995, cat. no. 4337.0
Children's Immunisation, Australia, 1995, cat. no. 4352.0
Disability, Ageing and Carers, Summary of Findings, Australia, 1998, cat. no. 4430.0
40 Current publications and other products released by the ABS are listed in the Catalogue of Publications and Products (cat. no. 1101.0). The Catalogue is available from any ABS office or the ABS web site. The ABS also issues a daily Release Advice on the web site which details products to be released in the week ahead.
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