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4 Non-Indigenous people were not eligible for selection in the supplementary Indigenous sample unless they were the parent or guardian of an Indigenous child and acted as spokesperson for the child (see below for further details).
5 The NHS(I) was designed to produce reliable estimates at the national level for persons in scope of the survey. The sample design was based on a broad dissection of Australia into non-sparsely settled and sparsely settled areas. The samples for non-sparsely settled areas and sparsely settled areas were designed separately with each involving a multistage sampling process. The 2001 NHS was designed to cover only non-sparsely settled areas. Therefore the Indigenous supplement provided both additional selections in these areas as well as the total Indigenous sample in sparsely settled areas.
6 Dwellings in non-sparsely settled areas were selected using a stratified multistage area sample. A number of Census collection districts (CDs) were randomly selected based on the number of dwellings containing Indigenous persons in the area as at the 1996 Census of Population and Housing. A random selection of dwellings within selected CDs were then screened to assess their usual residents' Indigenous status. Where a dwelling contained one or more Indigenous usual residents aged 18 years or more, one Indigenous adult (18 years of age or more) and up to two Indigenous children (0 to 17 years of age) were randomly selected to participate in the survey.
7 In sparsely settled areas, the sample was obtained from a random selection of discrete Indigenous communities and outstations across Australia using information collected in the 1999 Community Housing and Infrastructure Needs Survey (CHINS). Within selected communities and outstations a random selection of dwellings was made. Within selected dwellings, one Indigenous adult (18 years of age or more) and up to one Indigenous child (0 to 17 years of age) were randomly selected to participate in the survey.
8 For the non-sparsely settled area component of the supplementary survey, approximately 91% of households identified with in-scope Indigenous residents responded to the survey. This response rate does not take into account the 6.5% of households in the screened component of the sample that were unable to be contacted to establish the Indigenous status of the occupants. For the sparsely settled area component, approximately 87% of in-scope households responded to the survey.
9 Data collection was undertaken by ABS interviewers. Persons aged 18 years or more were interviewed personally, with the exception of persons who were too sick or otherwise unable to respond personally. Persons aged 15 to 17 years were interviewed with the consent of a parent or guardian; otherwise a parent or guardian was interviewed on their behalf. For persons aged less than 15 years, information was obtained from a person responsible for the child.
10 There were, however, a number of differences in the data collection methods in sparse and non-sparse areas. In non-sparsely settled areas, adult females were invited to complete a small additional questionnaire covering specific supplementary women's health topics. This additional questionnaire was voluntary and self-enumerated. Of the women invited to complete the supplementary questionnaire in non-sparsely settled areas, 91% responded.
11 In sparsely settled areas, standard household survey approaches were modified to take account of language and cultural issues. In addition, interviewers worked in teams of two, one male and one female, to collect the survey information. Male interviewers collected personal information from male respondents, and female interviewers collected personal information from female respondents. The interviewers were accompanied, wherever possible, by local Indigenous facilitators, preferably one male and one female, who assisted in the conduct and completion of the interviews. The Indigenous facilitators explained the purpose of the survey to respondents, introduced the interviewers, assisted in identifying the usual residents of a household and in locating residents who were not at home, and assisted respondent understanding of the questions where necessary.
12 In addition, the survey content in sparsely settled areas was limited to those topics for which data of acceptable quality could be collected. Some questions were reworded to assist respondents in understanding the concepts. Of the supplementary women's health topics that were collected with a self enumerated questionnaire in non-sparsely settled areas, in sparsely settled areas a subset was collected through personal interview with adult female respondents who were informed of the potential sensitivity and voluntary nature of these additional questions.
13 The NHS Indigenous supplementary sample was designed to obtain data on a wide range of health issues and to enable comparisons between the Indigenous and non-Indigenous populations.
The survey collected information about:
14 Specific topics included in the survey were:
15 The survey content for the Indigenous supplement to the NHS in non-sparsely settled areas is the same as the content included in the 2001 NHS, with the exception of mental health information which was not collected from the supplementary Indigenous sample. The Kessler Psychological Distress Scale 10 (K-10) module of questions used in the 2001 NHS was not considered to be culturally appropriate for the Indigenous population.
16 The content for the Indigenous supplement to the NHS in sparsely settled areas is a subset (approximately 50%) of the content collected in non-sparsely settled areas. The sparsely settled content was confined to those items for which acceptable data quality levels could be achieved.
17 For a full list of data items collected in non-sparsely settled and sparsely settled areas, refer to the National Health Survey: Users Guide, 2001 which will be available on the ABS web site in December 2002.
RELIABILITY OF ESTIMATES
18 The estimates in this publication are subject to sampling and non-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.
20 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. For more information on sampling error and its impact on interpreting results in this publication refer to the Technical Notes.
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 For details about the steps taken to minimise other non-sampling error, see paragraph 9 of the Technical Notes. For more details about non-sampling error see paragraphs 25 to 35 of these Explanatory Notes.
INTERPRETATION OF RESULTS
26 Reported information on long-term medical conditions was not medically verified, and was not necessarily based on diagnosis by a medical practitioner. Conditions which have a considerable effect on well-being or lifestyle are expected to be better reported than those which have little effect. Some people may be unaware of minor conditions, and occasionally may have serious conditions which have not been diagnosed.
27 There may be some instances of under-reporting as a consequence of respondents being unwilling to talk about a particular condition at an interview. Results of previous health surveys conducted by the ABS also suggest a tendency for respondents in the general population to under-report alcohol and tobacco consumption levels, underestimate their weight, and to over-estimate their height.
28 Information in this publication is presented by the Australian Standard Geographical Classification (ASGC) Remoteness Structure. Non-remote area estimates have been derived from data collected in non-sparsely settled areas by excluding a small component of non-sparse areas which are defined as remote in the ASGC Remoteness Structure. Similarly, estimates from remote areas have been derived from data collected in sparsely settled areas together with the small component of non-sparsely settled areas which are defined as remote.
29 As the content collected in sparsely settled areas was a subset of that collected in non-sparsely settled areas, not all data items are available for the total Indigenous population. In addition, no 1995 NHS data are available for remote areas restricting comparisons between Indigenous estimates for 1995 and 2001 to non-remote areas.
30 In both 1995 and 2001, all children of Aboriginal and/or Torres Strait Islander origin living in households in non-sparsely settled areas had a random chance of selection in the main NHS. Similarly, all such Indigenous children had a chance of selection in the Indigenous supplement to the 1995 NHS, as selected households in non-sparsely settled areas identified to have at least one usual resident of Aboriginal and/or Torres Strait Islander origin were enumerated.
31 However, in the 2001 Indigenous supplement to the NHS, selected households were screened to identify only those households where at least one adult (18 years or over) of Aboriginal and/or Torres Strait Islander origin was usually resident. Therefore, Indigenous children living in households in non-remote areas where there was no Indigenous adult usually resident (up to one quarter of all Indigenous children in non-remote areas reside in such households) did not have a chance of selection in the supplement.
32 Responses from the main sample and from the Indigenous supplement are weighted and then benchmarked to Indigenous population estimates (for age, sex, and area of usual residence) so that final survey estimates will be representative of the age and sex characteristics of the Indigenous population in different areas. However, it is possible that the health characteristics of Indigenous children living in households where there are no Indigenous adults may be different to those of Indigenous children of the same age and sex living in the same non-remote areas, but in households where Indigenous adults are resident. If such differences exist, it may mean that the survey results for Indigenous children under-represent these differences. However, in context of the relative standard errors for the estimates from the Indigenous component of the 2001 NHS, any differences due to such under-representation could in some cases affect the interpretation of results.
33 In the 2004-05 Indigenous Health Survey, field procedures will be changed to provide for adequate representation of Indigenous children in households with no resident Indigenous adult.
34 Other issues to be aware of when interpreting results from the NHS(I) include:
35 Many results presented in this publication have been adjusted for differences in the age structure between the Indigenous, non-Indigenous and total Australian populations to take account of the younger age profile of the Indigenous population. This age-standardisation has been undertaken using the direct method (see Technical Notes). Data which have been tabulated according to broad age groupings have not been age-standardised and hence the rates apply to the Indigenous and non-Indigenous populations without adjustments to account for the differing age structures. These rates, together with the total estimates presented in Appendix 1, can be used to calculate the actual population estimate for an item of interest. The ABS considers that comparisons of unadjusted rates within the broad age groups presented in this publication and would be little different if standardised within the age ranges.
36 Further information on the interpretation of results is contained in the National Health Survey: Users Guide, 2001, which will be available on the ABS web site in December 2002.
37 Major classifications used for items shown in this publication are:
38 Further information about these classifications is contained in the National Health Survey: Users Guide, 2001 which will be available on the ABS web site in December 2002.
COMPARABILITY WITH 1995 NATIONAL HEALTH SURVEY
39 This publication contains selected results from the Indigenous component of the 1995 NHS. These results are limited to topics where a reasonable level of comparability between the 1995 and 2001 data is expected. While the 2001 NHS is similar to the 1995 survey in many ways, there are important differences in sample design and coverage, survey methodology and content, definitions, etc. which affect the degree to which data are directly comparable between the surveys.
40 The main differences between the 1995 and 2001 collections, apart from the differences in field procedures discussed in paragraphs 30 to 32 above, which may affect the comparability of data presented in this publication are outlined below.
41 Due to the small size of the supplementary Indigenous samples in the 1995 and 2001 NHS, the Indigenous results from these surveys are not available below the national level and have a larger associated sampling error than results from many other ABS surveys. For this reason, differences in reported rates for 1995 and 2001 may or may not be statistically significant. Significance testing has been undertaken on selected Indigenous and non-Indigenous comparisons (table 1) and time series data (table 2) presented in the publication to assist readers with understanding the level of significance that should be attributed to apparent differences in rates. For further information about significance testing, please see the Technical Notes section of this publication.
42 Time series information for 1995 and 2001 presented in this publication is based on data for non-remote areas only due to concerns about the quality of remote area data collected in the 1995 survey. After an extensive investigation into Indigenous results from the 1995 collection, responses from people living in remote areas were excluded.
43 For further information about comparability between the 1995 and 2001 NHS see the National Health Survey, Users Guide, 2001 which will be available on the ABS web site in December 2002.
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