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3 The survey collected the following information from the three target populations:
4 The survey also collected a small amount of information about people not in the target populations.
5 The scope of SDAC was persons in both urban and rural areas in all states and territories, living in both private and non-private dwellings (including persons in cared-accommodation), but excluding:
6 The coverage of SDAC was the same as the scope except that the following (small) populations were not enumerated for operational reasons:
7 Rules were applied to maximise the likelihood that each person in coverage was associated with only one dwelling and thus had one chance of selection.
8 Usual residents of selected private dwellings and non-private dwellings (excluding persons in cared-accommodation) were included in the survey unless they were away on the night of enumeration and had been away or were likely to be away for seven months or more. This was designed to avoid multiple selection of a person who might be spending time, for instance, in a nursing home, to be eligible for selection there.
9 Visitors to private dwellings were excluded from coverage as the expectation was that most would have their chance of selection at their usual residence.
10 Occupants of cared-accommodation establishments in the scope of the survey were enumerated if they had been, or were expected to be, a usual resident of an establishment for three months or more.
11 Multi-stage sampling techniques were used to select the sample for the survey. After sample loss, the household sample included approximately 27,600 private dwellings and 200 non-private dwellings, while the cared-accommodation sample included approximately 1,100 establishments.
12 After exclusions due to scope and coverage, the final sample comprised 64,213 persons for the household component and 9,470 persons for the cared-accommodation component.
13 Different data collection methods were used for the household component and the cared-accommodation component.
14 The household component covered persons in:
15 Smaller disability homes (with fewer than six persons) were considered to be private dwellings.
16 In this publication, persons in the household component of the survey are referred to as 'living in households'.
17 The cared-accommodation component covered residents of hospitals, nursing homes, hostels and other homes such as children's homes, who had been, or were expected to be, living there or in another health establishment for three months or more.
18 Data for the household component of the survey were collected by trained interviewers, who conducted computer-assisted personal interviews.
19 A series of screening questions were asked of a responsible adult in a selected household to establish whether the household included:
20 Where possible, a personal interview was conducted with people identified in any of the above populations. Proxy interviews were conducted for:
21 People with a disability were asked questions relating to help and assistance needed and received for communication, mobility, self-care, cognition or emotion, health care, household chores, property maintenance, meal preparation, reading and writing tasks, and transport activities. They were also asked questions relating to their computer and Internet use and participation in community activities. Those aged 5 to 20 years (or their proxies) were asked about schooling restrictions, and those aged 15 to 64 years about employment restrictions.
22 People aged 60 years and over without a disability were asked questions about need for, and receipt of, help for household chores, property maintenance, meal preparation, reading and writing tasks, and transport activities. They were also asked questions relating to computer and Internet use and participation in community activities.
23 Persons who confirmed they were the primary carer of a person with a disability or an older person were asked about the assistance they provided, the assistance they could call on, and their employment experience. They were also asked to complete a self-enumeration form which collected information about their attitudes to, and experience of, their caring role.
24 Basic demographic and socio-economic information was collected for all people in the household. Most of this information was provided by a responsible adult in the household.
25 The cared-accommodation component was enumerated in two stages using a mail-based methodology directed to administrators of selected establishments.
26 The first stage required completion of a Contact Information Form to establish the name of a contact officer, the current number of occupants within the establishment and the type of establishment.
27 The second stage required the nominated contact officer to select occupants in their establishment, following the instructions provided. A separate questionnaire was completed for each selected occupant.
28 The range of data collected in the cared-accommodation component was smaller than in the household component as some topics were not suitable for collection through a paper questionnaire or were irrelevant to those residing in cared-accommodation.
WEIGHTING, BENCHMARKING and ESTIMATION
29 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 enumerated person. The weight is a value which indicates how many population units are represented by the sample unit.
30 The first step in calculating weights for each person is to assign an initial weight, which is 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 300, then the person would have an initial weight of 300 (that is, they represent 300 people).
31 The responses from persons in the cared-accommodation component and persons in the private dwelling and non-cared accommodation components of the survey were weighted together in order to represent the entire in-scope population.
32 The weights were calibrated to align with independent estimates of the population, referred to as benchmarks, in designated categories of sex by age by area of usual residence. Weights calibrated against population benchmarks ensure that the survey estimates conform to the independently estimated distribution of the population rather than to the distribution within the sample itself. Calibration to population benchmarks helps to compensate for over or under-enumeration of particular categories of persons which may occur due to either the random nature of sampling or non-response.
33 The survey was benchmarked to the estimated resident population (ERP) in each state and territory, excluding those living in very remote areas of Australia, at 30 June 2009. The SDAC estimates do not (and are not intended to) match estimates for the total Australian population obtained from other sources (which may include persons living in very remote parts of Australia).
34 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.
35 Totals presented in tables comparing rates over time are shown as age-standardised percentages. Age standardisation has been undertaken using the direct method (see Technical Note). An age-standardised rate removes the effects of different age structures when comparing population groups or changes over time. A standard age composition is used, in this case the age composition of the 30 June 2001 ERP. The standardised rate is that which would have prevailed if the actual population had the standard age.
RELIABILITY OF ESTIMATES
36 All sample surveys are subject to error which can be broadly categorised as either:
37 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.
38 Non-sampling error may occur in any 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 answers by interviewers, and errors in coding and processing data. Every effort was made to reduce the non-sampling error by careful design and testing of the questionnaire, training and supervision of interviewers, follow-up of respondents, and extensive editing and quality control procedures at all stages of data processing.
INTERPRETATION OF RESULTS
39 Disability is a difficult concept to measure because it depends on a respondent's perception of their ability to perform a range of activities associated with daily living. Factors discussed below should also be considered when interpreting the estimates contained in this publication.
40 Information in the survey was based, wherever possible, on the personal response given by the respondent. However, in cases where information was provided by another person, some answers may differ from those the selected person would have provided. In particular, interpretation of the concepts of 'need' and 'difficulty' may be affected by the proxy-interview method.
41 A number of people may not have reported certain conditions because of:
42 As certain conditions may not have been reported, data collected from the survey may have underestimated the number of people with one or more disabilities.
43 The need for help may have been underestimated as some people may not have admitted needing help because of such things as a desire to remain independent, or may not have realised help was needed with a task because help had always been received with that task.
44 The criteria by which people assessed whether they had difficulty performing tasks may have varied. Comparisons may have been made with the ability of others of a similar age, or with the respondent's own ability when younger.
45 The criteria used to identify disability and disability status has not changed between 2003 and 2009.
46 The different collection methods used (personal interview for households, and administrator completed forms for cared-accommodation) may have had some effect on the reporting of need for assistance with core activities. As a result there may have been some impact on measures such as disability status. If so, this would have more impact on the older age groups because of their increased likelihood of being in aged care-accommodation.
MAKING COMPARISONS BETWEEN SURVEYS OVER TIME
47 Much of the content of the six disability surveys conducted by the ABS in 1981, 1988, 1993, 1998, 2003 and 2009 is comparable. There are differences, however, as later surveys have attempted to obtain better coverage of disability and of specific tasks and activities previously considered too sensitive for a population survey.
CHANGES TO CLASSIFICATIONS
48 In 2006, the Australian and New Zealand Standard Classification of Occupations (ANZSCO) (cat. no. 1220.0) replaced the Australian Standard Classification of Occupations (ASCO) Second Edition, 1997 (cat. no. 1220.0) and the New Zealand Standard Classification of Occupations (NZSCO), 1999 used in Australia and New Zealand, respectively. ANZSCO provides an integrated framework for storing, organising and reporting occupation-related information.
49 Further information about SDAC including a list of data items included in the survey will be included in Disability, Ageing and Carers: User Guide, Australia, 2009 (cat. no. 4431.0.55.001), expected to be released on the ABS website in June 2011.
50 All data in this publication are available in a Data Cube (spreadsheet format).
51 It is expected that both a basic and an expanded confidentialised unit record file (CURF) will be produced from the SDAC, subject to the approval of the Australian Statistician. The expanded CURF will contain more detail than the basic CURF and will only be available via the Remote Access Data Laboratory (RADL), which is a secure Internet-based data query service. The basic CURF will be available via CD ROM or RADL.
52 Previous ABS publications relating to disability, ageing and carers:
Disability, Ageing and Carers, Australia: Summary of Findings, 2009 (cat. no. 4430.0)
ABS Sources of Disability Information, 2003-2008 (cat. no 4431.9.55.002)
Social Participation of People with a Disability, 2011 (cat. no. 4439.0)
Disabiity, Vocation and Education Training, 2009 (cat. no. 4438.0)
Aspects of Health and Disability in Australia, 2007-2008 (cat. no. 4367.0)
A Profile of Carers in Australia, 2008 (cat. no. 4448.0)
People with a Need for Assistance - A Snapshot, 2006 (cat. no. 4445.0)
Disability, Australia, 2003 (cat. no. 4446.0)
Disability, Ageing and Carers: User Guide, Australia, 2003 (cat. no. 4431.0.55.001)
Census of Population and Housing: Ageing in Australia, 2001 (cat. no. 2048.0)
Caring in the Community, 1998 (cat. no. 4436.0)
Disability and Disabling Conditions, 1998 (cat. no. 4433.0)
Disability, Ageing and Carers, Australia: Disability and Disabling Conditions, 1993 (cat. no. 4433.0)
Disability, Ageing and Carers, Australia: Visual Impairment, 1993 (cat. no. 4434.0)
Disability, Ageing and Carers, Australia: Hearing Impairment, 1993 (cat. no. 4435.0)
Disability, Ageing and Carers, Australia: Brain Injury and Stroke, 1993 (cat. no. 4437.0).
53 Other ABS publications which may be of interest include:
Australian Social Trends (cat. no. 4102.0)
Labour Force, Australia (cat. no. 6202.0)
Education and Training Experience, Australia, 2009 (cat. no. 6278.0)
Private Hospitals, Australia, 2009-2010 (cat. no. 4390.0)
National Aboriginal and Torres Strait Islander Social Survey, 2008 (cat. no. 4714.0)
Household Income and Income Distribution, Australia, 2007-08 (cat. no. 6523.0)
National Health Survey: Summary of Results, 2007-08 (cat. no. 4364.0)
General Social Survey: Summary Results, Australia, 2006 (cat. no. 4159.0)
How Australians Use Their Time, 2006 (cat. no. 4153.0).
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