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5 In addition, the broader survey collected a wide range of information about selected health conditions, risk factors (for example, obesity) and demographic and socioeconomic factors, which can be analysed in relation to the NATSIHMS results.
6 The list of data items from the survey, as well as detailed information on the different tests used in the NATSIHMS, is available in the Australian Aboriginal and Torres Strait Islander Health Survey: Users' Guide, 2012–13 (cat. no. 4727.0.55.002).
SCOPE OF THE SURVEY
7 The 2012–13 NATSIHS and NATSINPAS included a combined sample of 8,237 private dwellings across Australia. Remote and non-remote areas in all states and territories were included, as were discrete Aboriginal and Torres Strait Islander communities.
8 The scope was all Aboriginal and Torres Strait Islander people who were usual residents of private dwellings in Australia. Usual residents are those who usually live in a particular dwelling and regard it as their own or main home.
9 Private dwellings are houses, flats, home units and any other structures used as private places of residence at the time of the survey. People usually resident in non-private dwellings, such as hotels, motels, hostels, hospitals, nursing homes, and short-stay caravan parks were not in scope. This may affect estimates of the number of people with some conditions; for example, conditions which may require periods of hospitalisation, such as kidney disease.
10 Further scope exclusions for this survey were:
12 The interview components of the NATSIHS and NATSINPAS were conducted under the Census and Statistics Act (CSA) 1905. The biomedical component was collected under the Privacy Act 1988 and were subject to ethics approval. Ethics approval for the NATSIHMS at the national level was sought and gained from Australian Government Department of Health and Ageing’s Departmental Ethics Committee.
13 Ethics approval for the NATSIHMS component was also required at the jurisdictional level for New South Wales, Western Australia, Northern Territory and for Queensland Health Service Districts. Ethics approval was sought and gained from the following Ethics Committees:
15 Informed consent was sought from adults through completion of a consent form. A copy of the consent form was left with the respondent. Those that agreed to take part were provided a referral form to complete (including whether specific medications or supplements were regularly taken) to provide to the collection clinic.
16 A follow-up reminder process was used for non-remote respondents who consented to the NATSIHMS but had not yet attended a collection clinic. This process took the form of phone calls or letters arranged ten days apart from the interview date. Home visits and temporary clinics were offered to participants in certain circumstances to maximise participation rates, particularly in remote areas and for those who were incapacitated. To reduce expenses for travel, child-care or time off work, all participants were able to claim a reimbursement of $50.
17 Most blood and urine samples were collected at Sonic Healthcare collection clinics or alternatively, via a home visit or temporary clinic held at Aboriginal Medical Services (AMS) using standard operating procedures for phlebotomy collection. In some areas, other pathology service providers were used (including IMVS Pathology for regional areas in South Australia and Northern Territory), but the same standard collection procedures were still used.
18 All blood and urine samples, with the exception of urinary Iodine analysis, which was conducted by Sullivan Nicolaides Pathology (SNP) in Queensland, were then analysed at a central laboratory at Douglass Hanly Moir (DHM) Pathology in Sydney, Australia on machines accredited by the National Association of Testing Authorities (NATA). DHM conducted Internal Quality Control (QC) analysis for all instruments used to conduct analysis on the samples. More information on NATSIHMS quality assurance methods and procedures is available in the Australian Aboriginal and Torres Strait Islander Health Survey: Users' Guide, 2011–13 (cat. no. 4727.0.55.002).
19 All participants were provided with a pathology report of their results either via post or through their local health service. Participants in non-remote areas could also nominate for their results to be sent to their regular doctor. In cases where the results were outside the normal range, participants were contacted by a qualified health professional and encouraged to discuss their results with their doctor. If the test results showed a significantly high or low result which was dangerous to the person's health, they were contacted immediately and advised on the best course of action.
20 In the NATSIHS and NATSINPAS combined, there were a total of 8,237 households fully responding, giving a response rate of 79.5%. This resulted in a total of 12,947 persons in the sample aged 2 years and over.
21 Of the 8,157 respondents aged 18 years and over in the combined NATSIHS/NATSINPAS sample, 3,293 (40.4%) participated in the biomedical component. A higher level of response was achieved in remote areas (55.8%) than in non-remote areas (28.1%).
RESPONSE RATES, National Aboriginal and Torres Strait Islander Health Measures Survey, 2012-13
NON- REMOTE/REMOTE RESPONSE RATES, National Aboriginal and Torres Strait Islander Health Measures Survey, 2012-13(a)
23 The following table compares characteristics of persons who participated in the NATSIHMS with those who participated in the NATSIHS and NATSINPAS combined.
COMPARISONS BETWEEN NATSIHMS AND NATSIHS/NATSINPAS SAMPLES, Persons aged 18 years and over, 2012–13
24 More detailed information on response rates is available in the Australian Aboriginal and Torres Strait Islander Health Survey: Users' Guide, 2011–13 (cat. no. 4727.0.55.002)
WEIGHTING, BENCHMARKING AND ESTIMATION
25 Weighting is a process of adjusting results from a sample survey to infer results for the in-scope total population. To do this, a weight is allocated to each sample person. The weight is a value which indicates how many population units are represented by the sample unit.
26 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). An adjustment was then incorporated into the weighting to account for Aboriginal and Torres Strait Islander persons not covered by the sample. For more information on undercoverage, see the Australian Aboriginal and Torres Strait Islander Health Survey: Users' Guide, 2012–13 (cat. no. 4727.0.55.002).
27 The weights are 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. 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. The selection of benchmarks was chosen to maximise the accuracy of the estimates of biomedical characteristics, by reducing both random and systematic errors as much as possible.
28 The NATSIHMS results were benchmarked to the estimated Aboriginal and Torres Strait Islander resident population living in private dwellings at 30 June 2011. Excluded from these benchmarks were persons in non-private dwellings. The benchmarks, and hence the estimates from the survey, do not (and are not intended to) match estimates of the total Australian Aboriginal and Torres Strait Islander resident population obtained from other sources.
29 Survey estimates of counts of persons are obtained by summing the weights of persons with the characteristic of interest. Estimates of non-person counts (for example, number of conditions) are obtained by multiplying the characteristic of interest with the weight of the reporting person and aggregating.
30 The weights for the NATSIHMS are different to the weights for the combined NATSIHS/NATSINPAS due to the differing response patterns between the surveys.
31 An investigation was undertaken to determine whether the accuracy of NATSIHMS estimates could be improved by weighting with any other variables collected in the NATSIHS and NATSINPAS, including smoking status, Body Mass Index, self-assessed health, employment status, marital status and blood pressure. While the use of some of these variables would have improved the accuracy of some NATSIHMS estimates (e.g. the use of smoker status in the weighting process would have ensured that totals relating to current daily smokers were identical in the NATSIHMS to those in the combined NATSIHS and NATSINPAS), they made no difference to the main variables of interest in the NATSIHMS (i.e. estimates of diabetes, cholesterol) and even in some cases increased the measure of sampling error or Relative Standard Error (RSE).
32 The decision to maximise the accuracy of these main variables of interest in the NATSIHMS by not including those other variables in the calculation of weights for the NATSIHMS means that, while variables collected in the NATSIHMS can be analysed with variables collected in either the NATSIHS and NATSINPAS, the NATSIHS and NATSINPAS should be used when reporting on the prevalence of these variables. For example, for self-reported medical conditions and risk factors such as smoking, the most accurate prevalences should be calculated using the combined NATSIHS and NATSINPAS sample.
RELIABILITY OF ESTIMATES
Sampling and non-sampling error
33 All sample surveys are subject to sampling and non-sampling error.
34 Sampling error is the difference between 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. Indications of the level of sampling error are given by the Relative Standard Error (RSE) and Margin of Error (MoE).
35 In this publication, estimates with an RSE of 25% to 50% are preceded by an asterisk (e.g. *3.4) to indicate that the estimate has a high level of sampling error relative to the size of the estimate, and should be used with caution. Estimates with an RSE over 50% are indicated by a double asterisk (e.g. **0.6) and are generally considered too unreliable for most purposes. These estimates can be used to aggregate with other estimates to reduce the overall sampling error.
36 The MoEs are provided for all proportions to assist users in assessing their reliability. Users may find this measure is more convenient to use, rather than the RSE, in particular for small and large proportions. The proportion combined with the MoE defines a range which is expected to include the true population value with a given level of confidence. This is known as the confidence interval. This range should be considered by users to inform decisions based on the proportion.
37 Non-sampling error may occur in any data collection, whether it is based on a sample or a full count such as a census. Non-sampling errors occur when survey processes work less effectively than intended. Sources of non-sampling error include non-response or missing test results, errors in reporting by respondents or in recording of answers by interviewers, and occasional errors in coding and processing data.
38 Non-response can affect the reliability of results and can introduce a bias. The magnitude of any bias depends on 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.
39 Results for biomarkers may vary depending on the type of test and assay used, as well as the type of machine used to analyse the blood and urine samples. Details around the procedures followed for each of the biomarkers in the NATSIHMS are outlined in the Australian Aboriginal and Torres Strait Islander Health Survey: Users' Guide, 2012–13 (cat. no. 4727.0.55.002).
40 In the NATSIHMS, month of collection was used to analyse the seasonal effects of Vitamin D deficiency. Although there were proportionally more people who had their blood samples taken in Spring than in Autumn, this only had a very small impact on the overall rate of Vitamin D deficiency at the population level.
DISTRIBUTION OF THE ADULT NATSIHMS SAMPLE BY SEASON
41 The Census and Statistics Act, 1905 provides the authority for the ABS to collect statistical information, and requires that statistical output shall not be published or disseminated in a manner that is likely to enable the identification of a particular person or organisation. This requirement means that the ABS must take care and make assurances that any statistical information about individual respondents cannot be derived from published data.
42 Some techniques used to guard against identification or disclosure of confidential information in statistical tables are suppression of sensitive cells, random adjustments to cells with very small values, and aggregation of data. To protect confidentiality within this publication, some cell values may have been suppressed and are not available for publication but included in totals where applicable. As a result, sums of components may not add exactly to totals due to the confidentialisation of individual cells.
43 Estimates presented in this publication have been rounded. As a result, sums of components may not add exactly to totals.
44 Proportions presented in this publication are based on unrounded figures. Calculations using rounded figures may differ from those published.
45 The success of the 2012–13 AATSIHS was dependent on the very high level of cooperation received from Aboriginal and Torres Strait Islander Australians. Their continued cooperation is very much appreciated; without it, the range of statistics published by the ABS would not be possible. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act, 1905.
46 The 2012–13 AATSIHS was developed with the assistance of an advisory group comprised of experts on health issues, many of whom were Aboriginal and Torres Strait Islander people. The biomedical component was also developed with the assistance of several advisory groups and expert panels. Members of these groups were drawn from Commonwealth and state/territory government agencies, non-government organisations, relevant academic institutions and clinicians. The valuable contributions made by members of these groups are greatly appreciated.
PRODUCTS AND SERVICES
47 Summary results from the NATSIHMS are available in spreadsheet form from the Downloads tab in this release.
48 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. A list of data items is available from the Australian Aboriginal and Torres Strait Islander Health Survey: Users' Guide, 2011–13 (cat. no. 4727.0.55.002).
49 Other ABS publications which may be of interest are shown under the 'Related Information' tab of this release.
50 Current publications and other products released by the ABS are listed on the ABS website <www.abs.gov.au>. The ABS also issues a daily Release Advice on the website which details products to be released in the week ahead.
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