INTRODUCTION
1 This publication contains preliminary results from the 2003 Survey of Disability, Ageing and Carers (SDAC) conducted throughout Australia from 23 June to 1 November 2003.
SCOPE OF THE SURVEY
2 The survey covered people in both urban and rural areas in all states and territories, except for those living in remote and sparsely-settled parts of Australia.
3 The survey included people in both private and non-private dwellings, including people in cared accommodation but excluding those in gaols and correctional institutions.
4 The scope of the survey was all persons except:
- visitors to private dwellings
- certain diplomatic personnel of overseas governments, customarily excluded from the Census and estimated resident population figures
- overseas residents in Australia
- members of non-Australian defence forces (and their dependants) stationed in Australia.
5 Coverage rules were applied which aimed to ensure that each person in scope was associated with only one dwelling and thus had only one chance of selection.
6 Usual residents of selected private dwellings 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 four months or more. This was designed to avoid multiple selection of a person who might be spending time, for instance, in a nursing home, and be eligible for selection there.
7 Visitors to private dwellings were excluded as the expectation was that most would have their chance of selection at their usual residence.
8 Boarding school pupils were excluded from coverage but other persons in non-private dwellings in the scope of the survey were included if they had lived there, or were likely to live there, for four months or more.
9 Occupants of cared accommodation in the scope of the survey were included if they had been, or were expected to be, a usual resident of an establishment for three months or more.
DATA COLLECTION
10 Different data collection methods were used for the household component and the cared-accommodation component of this survey.
11 The household component covered people in:
- private dwellings such as houses, flats, home units, townhouses, tents and other structures used as private places of residence at the time of the survey
- non-private dwellings such as hotels, motels, boarding houses, educational and religious institutions, guest houses, construction camps, short-term caravan parks, youth camps and camping grounds, including staff quarters, and self-care components of retirement villages.
12 Smaller disability group homes (with fewer than six people) were considered to be private dwellings.
13 In this publication, people in the household component of the survey are referred to as 'living in households'.
14 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 at least three months.
Household component
15 Data for the household component of the survey were collected by trained interviewers, who conducted computer-assisted personal interviews.
16 A series of screening questions were asked of a responsible adult in a selected household to establish whether the household included:
- people with a disability
- people aged 60 years or more
- people who were primary carers for older people and/or people with a disability, living either in the same household or elsewhere, or who provided any care to persons living elsewhere.
17 Where possible, a personal interview was conducted with people identified in any of the above populations. Proxy interviews were conducted for children under 15, those aged 15-17 whose parents did not permit them to be personally interviewed, and those with a disability that prevented them from having a personal interview.
18 People with a disability were asked questions relating to help and assistance needed and received for self-care, mobility, communication, cognitive and emotional support, health care, housework, property maintenance, meal preparation, paperwork (reading and writing tasks) and transport activities. Those aged 5-20 years (or their proxies) were asked about schooling restrictions, and those aged 15-64 years about employment restrictions.
Cared-accommodation component
19 The cared-accommodation component was enumerated in two stages using a mail-based methodology directed to administrators of selected establishments.
20 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.
21 The second stage required the nominated contact officer to select occupants, following the instructions provided. A separate questionnaire was completed for each person meeting the coverage requirements.
22 The range of data collected in this component was smaller than in the household component as some topics were not suitable for collection through a mail-based methodology or were irrelevant to those residing in cared accommodation.
SURVEY DESIGN
Sample size and collection
23 Multi-stage sampling techniques were used to select the sample for the survey. After sample loss, the household sample included approximately 14,000 private dwellings and 300 non-private dwelling units, while the cared accommodation sample included approximately 550 establishments.
24 After exclusions due to scope and coverage, the final sample comprised 36,241 people for the household component and 5,145 people for the cared-accommodation component.
WEIGHTING, BENCHMARKING AND ESTIMATION
Weighting
25 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.
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).
Benchmarking
27 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. 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.
28 The survey was benchmarked to the estimated population living in non-sparsely settled areas at 30 June 2003 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
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 (e.g. days away from work) are obtained by multiplying the characteristic of interest with the weight of the reporting person and aggregating.
Standardisation
30 Some data for time series tables contained in this publication are shown as age-standardised estimates or percentages. Many disability 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 2003 SDAC population, i.e. the population at 30 June 2003 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
31 The estimates provided in this publication are subject to sampling and non-sampling error.
Sampling error
32 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.
Non-sampling error
33 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 of answers by interviewers, and errors in coding and processing data.
34 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 non-respondents' characteristics and those of people who responded to the survey.
35 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.
36 Every effort was made to reduce other non-sampling error to a minimum by careful design and testing of the questionnaire, training of interviewers and data-entry staff, and extensive editing and quality control procedures at all stages of data processing.
INTERPRETATION OF RESULTS
37 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.
38 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.
39 A number of people may not have reported certain conditions because of:
- the sensitive nature of the condition (e.g. alcohol and drug-related conditions, schizophrenia, mental retardation or mental degeneration)
- the episodic or seasonal nature of the condition (e.g. asthma, epilepsy)
- a lack of awareness of the presence of the condition on the part of the person reporting (e.g. mild diabetes) or a lack of knowledge or understanding of the correct medical terminology for their condition, or
- the lack of comprehensive medical information kept by their cared-accommodation establishment.
40 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.
41 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.
42 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.
43 The criteria used to identify disability and disability status has not changed between 1998 and 2003. To remove the effect of change in the age structures of the population at those times, age-standardised disability rates have been included in Tables 1 and 2.
44 There was a 24% decrease in the number of persons in cared accomodation between 1998 and 2003. The different collection methods used - personal interview for households, and administrator completed forms for cared accomodation - 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 had more impact on the older age groupings because of their increased likelihood of being in aged care accomodation.
SDAC PRODUCTS AND SERVICES
Publications
45 Further information about SDAC will be included in Disability, Ageing and Carers: Summary of Findings, Australia, 2003 (cat. no. 4430.0) and Disability, Ageing and Carers: User Guide, Australia, 2003 (cat. no. 4431.0), expected to be released in September and October 2004 respectively.
Microdata
46 It is expected that a Confidentialised Unit Record File (CURF) will be produced from the SDAC, subject to the approval of the Australian Statistician.
Special tabulations
47 As well as releasing publications and standard products, the ABS can make available special tabulations. As this publication contains preliminary data only, special tabulations will not be available until the release of the final estimates in September 2004. When available, and 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 form, or in spreadsheets sent by email or on disk.
Other products
48 Further information on the survey and associated products is available from the contact officer listed at the front of this publication.
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