INTERPRETATION OF RESULTS
As noted in the Data Quality section, a range of factors have impacted on the quality of the data collected. The ABS has sought to minimise the effects of these factors through various means in the development and conduct of this survey, however, only sampling error can be quantified to allow users of the data to adjust for possible errors when using/interpreting the data. Information is not available from the survey to enable the effects of other issues affecting the data to be quantified. The relative importance of these factors will differ between topics, between items within topics, and by characteristics of respondents.
Comments have been included in individual topic descriptions in this publication to alert users of the data to the more significant issues likely to affect results for that topic, or items within it. These notes reflect ABS experience of past health and other surveys, feedback from users of data from those surveys, and ABS and other research on survey methods and response patterns, as well as information from survey testing and validation. However, they are indicative only, and do not necessarily reflect all factors impacting results, nor the relative importance of those factors.
Against this background, the following general comments are provided about interpreting data from the surveys.
- The surveys aim to provide statistics which represent the population or component groups of the population. It does not aim to provide data for analysis at the individual level. While errors of the types noted above may occur in individual respondent records, they will have little impact on survey estimates unless they are repeated commonly throughout the respondent population.
- The survey data are mainly self-reported and may differ from data sources that have different collection methodologies (e.g. administrative data), however, the AHS is able to provide dimensions of the data (e.g. population group, related health characteristics, use or non-use of other health services) and cross-classifications (e.g. self-assessed health by alcohol risk level) which are not available from administrative sources.
- Some survey topics, such as alcohol consumption in the National Health Survey (NHS), have some known data quality issues. While this means the data should be interpreted with care, the information is still considered valuable for certain uses. For example, while the overall levels of alcohol consumption described by the survey should be interpreted with caution, the data is still considered useful in describing consumption patterns across days of the week, types of drink consumed, relative levels of consumption across population groups, and alcohol consumption in relation to other risk behaviours or characteristics. It is also useful for monitoring changes in the levels and patterns of consumption over time. Information regarding any known data quality issues are contained in the individual topic descriptions in this Users' Guide.
- Although various reference periods are used throughout the survey for different topics (e.g. current, usual, last week, last 2 weeks, last 4 weeks) the survey essentially provides a 'point in time' picture of the health of the population and of population sub-groups. That is, the survey provides information about the prevalence of characteristics, not the incidence of those characteristics or of changes in characteristics (except in terms of differences between surveys). As the surveys were conducted over two separate 12 month periods, the results are essentially an average over that period, that is, representative of a typical week, fortnight, etc. in that period.
Factors specific to the nutrition results of 2011-12 NNPAS are discussed in the Interpretation of Results
section within the Nutrition
chapter of this Users' Guide. Factors specific to the biomedical results of 2011-12 NHMS are discussed within the Biomedical Measures
chapter of this Users' Guide.
Comparability between 2011-12 National Health Survey (NHS) and National Nutrition and Physical Activity Survey (NNPAS)
The AHS general population wave comprises two surveys. Results from the NHS and NNPAS samples are available separately or as part of a combined sample. Use of the separate files allows analysis of content that was collected as part of the individual surveys, some of which are common between the surveys and some which is unique to the particular survey. Data in the Australian Health Survey: Updated Results, 2011-12
(4364.0.55.003) released on the 7 June 2013 is from the combined data file (referred to as the Core). With a larger sample size (approximately 32,000 people), the Core provides more accurate estimates and allows for analysis at a finer level of disaggregation.
As the two surveys and the combined sample have different sample sizes and have been weighted separately to population benchmarks only, survey estimates of common items between the three files may vary slightly. For example, the estimates for current daily smoker may vary between the NHS, NNPAS and the combined Core sample. When using data from these files, it is important to understand and reference the source of the data. In terms of Core data items, the full sample in the Australian Health Survey: Updated Results, 2011-12 (4364.0.55.003) will provide the most accurate estimates. For more information on the structure of the AHS, see the Structure of the Australian Health Survey page of this Users' Guide.
Common content between NHS and NNPAS
The 2011-12 NHS and NNPAS were developed as part of the suite of AHS surveys.
While the NHS and the NNPAS are two independent samples, a large proportion of content is common between the two. The Core sample consists of these common items for the combined NHS and NNPAS samples. Results for a wide range of NHS items including these common items were published using the NHS sample only in the Australian Health Survey: First Results, 2011-12
(4364.0.55.001) publication. Results for these common items using the larger core sample have been published in the Australian Health Survey: Updated Results, 2011-12
(4364.0.55.003) publication. This publication and combined sample survey files should be used for all investigations on the common content only.
Common content is also available on the individual survey files. This enables comparison of this common content with both NHS only items and NNPAS only items, however it will not be possible to compare NHS only and NNPAS only items. For example, it is possible on the NHS file to compare fruit and vegetable consumption (common) with alcohol risk levels (NHS only), and on the NNPAS file to compare fruit and vegetable intake (common) with type of diet currently on (NNPAS only). However it is not possible on any file to compare alcohol risk levels with type of diet currently on.
The following tables summarises the common modules between the 2011-12 NHS and NNPAS surveys. Where content within these modules is common, these items will be available on the combined sample file.
Common survey modules
|Topics covered||Common items available from 2011-12 NHS and NNPAS ||Main differences between NHS and NNPAS |
|General demographics||Sex; age; marital status (registered & social); Indigenous status; country of birth (of respondent and mother/father); year of arrival in Australia; main language spoken at home; proficiency in English; family type; household size, composition, type; geographic location||NHS collected ancestry|
|Education||Highest year of school completed; whether has non-school qualification; level of highest non-school qualification; main field of non-school qualification obtained; whether currently studying full or part time ||NHS collected location, level and main field of current study|
|Labour force||Labour force status; status in employment; occupation, industry and industry sector of main job; hours worked; duration of unemployment; shift work||NHS collected whether ever served in the Australian Defence Force|
|Income||Household income gross weekly, equivalised ||NHS collects personal income|
|Health conditions||Self-assessed health; Female life stages; Diagnosis status of: Heart and circulatory conditions, Diabetes/high sugar levels, Kidney disease||NHS collected additional action related details for conditions as well as collecting more extensive listing of conditions|
|Body mass||Body mass index and measured height, weight and waist circumference measurements; Self-perceived weight||NHS collected perceived weight change in last year; NNPAS collected type of diet currently on and satisfaction with current weight|
|Dietary behaviours||Usual daily intake of vegetables & fruit and use of salt and whether it is iodised||NHS collected type of milk usually consumed and fat content of milk; NNPAS collected type of foods avoided due to allergies/intolerance/cultural, religious or ethical reasons|
|Smoking||Smoker status||NHS collected number of smokers in household, age started/stopped smoking regularly|
|Adult Exercise/Physical Activity||Type, frequency and duration of exercise/physical activity in last week; exercise level; whether met guidelines; sufficient activity measure; whether walked for transport; number of times walked, did moderate or vigorous exercise/physical activity and total duration for each||Some question wording (e.g. exercise versus physical activity) and ordering differences between surveys for the physical activity component of the module. NNPAS collected strength and toning. Sedentary data is not comparable between surveys|
Survey specific topics include:
- NHS Only – Breastfeeding, alcohol consumption, healthy lifestyles, use of medications, family stressors, financial stress, private health insurance and housing details
- NNPAS Only – 24 hour dietary recall, pedometer steps, child physical activity (2-4 and 5-17) and food security.
For further general information regarding common and survey specific topics, refer to the Structure of the Australian Health Survey
page in this Users’ Guide.
Comparability between 2011-12 NHS and 2007-08 NHS
Understanding the comparability of data from the 2011-12 NHS with data from previous NHS cycles is important for the use of those data and interpretation of apparent changes in health characteristics over time. While the 2011-12 NHS is deliberately the same or similar in many ways to the 2007-08, 2004-05 and 2001 NHS cycles (and in part to the 1995 NHS), there are important differences in sample design and coverage, survey methodology, content, definitions and classifications between the surveys. These differences will affect the degree to which data are directly comparable between the surveys, and hence the interpretation of apparent changes in health characteristics over the 2007-08 to 2011-12 period.
Throughout the topic descriptions and in other parts of this publication, comments have been made about the changes between surveys and their expected impact on the comparability of data. These are general comments based on results of testing, ABS experience in survey development, and preliminary examination of data from the 2011-12 survey. They should not, therefore, be regarded as definitive statements on comparability, and they may omit the types of findings which might result from a detailed analysis of the effects of all changes made.
The following table summarises key differences in the general survey characteristics of the 2007-08 to 2011-12 surveys:
The overall sample of households was about 1.4% lower in 2011-12 than in 2007-08 with the same proportion of people in each household enumerated. This resulted in the total sample of persons in the 2011-12 survey being only slightly below that of 2007-08. The impact of the lower sample size on the RSEs of the NHS 2011-12 will be minimal.
Differences in the reliability of estimates between surveys should be considered in interpreting apparent changes between the surveys. It is recommended that apparent changes are significance tested (see 'Testing for statistically significant differences' in the Data Quality
section of this chapter).
Through the weighting process, weighted survey estimates for state by part of state by sex by broad age group will be the same or very similar to the benchmark populations. However, because the characteristics of the sample are not identical to those of the benchmark population, some records will receive higher or lower weights than others. As this will vary between surveys, it is a factor to consider in comparing 2011-12 with 2007-08 data, but the impact on comparability is expected to be small. Sample and population figures for the two surveys appear in the following table:
(a) Benchmark population as at 31 October 2011.
(b) Benchmark population as at 31 December 2007.
Partial enumeration of households
|2011-12 NHS(a) ||2007-08 NHS(b) |
% of adults in sample
% of adults in population
% of adults in sample
% of adults in population
|75 and over |
Prior to 2001, all persons in sampled dwellings were select in the survey and only records from fully responding households were retained on the data file. This meant that results could be compiled at household, family and income unit level, in addition to person level. The 2001, 2004-05, 2007-08 and 2011-12 cycles, however, sub-sampled persons in households (one adult and one child 0-17 years), therefore complete enumeration occurs only in a minority of households.
Basic demographic characteristics were collected from a responsible adult in the household about all household members, such as age, sex, country of birth and year of arrival. This data is available on the 'All Persons' level to allow household composition variables to be calculated, such as 'Number of male adults in household', 'Number of non-Australian household members' etc. Some information about the household was also collected from the selected adult, including 'number of daily smokers in the household', 'household income', 'tenure type' and 'dwelling characteristics'. While these items were collected as part of the selected adult interview, they are available on the household level in 2011-12. This is the same in 2007-08, other than 'number of daily smokers in the household', which is on the person level.
Comparability of 2011-12 NHS data with 2007-08 NHS
For the majority of the survey, data is comparable between 2007-08 and 2011-12 surveys due to common questions and methodologies used.
However, there are a number of issues affecting comparability of data between the 2007-08 and 2011-12 surveys. Some examples of these include:
- Some modules contain additional questions and/or have had questions removed. General details on this is available at the end of each topic page of this Users' Guide.
- The 2011-12 survey made use of trigram coders where a question contained a list of possible answers plus an 'other' category. Where the interview could not find a response in the trigram they were then sequenced to a text field for later coding. In the 2007-08 survey, the 'other' category took the interviewers directly to a text field and these text responses were then later coded in the office.
- In 2011-12, a specific Kidney disease module was included in the survey for the first time. Therefore, kidney disease data is not directly comparable to previous surveys given the change in collection methodology.
- Additional types of health workers were collected in the Healthy Lifestyles module which were not included in the 2007-08 survey.
- Respondents use of medication was not collected in modules relating to specific medical or mental health conditions in the 2011-12 survey (with some exceptions, including mental and behavioural conditions, asthma, and some diabetes medication). Respondents were asked to provide details of all medications that they were taking regardless of what condition they were taking the medicine for. In the 2007-08 NHS survey respondents were asked about what medications they were taking for each specific medical or mental health condition.
- The reported prevalence of illness is complex and dynamic, and is a function of respondent knowledge and attitudes, which in turn may be affected by the availability of health services and health information, public education and awareness, accessibility to self-help, etc. For example, a public education program has been running in Australia over a number of years aimed to raise public awareness and public acceptance of mental health disorders. Consequently, respondents may be more willing to talk about or report feelings of anxiety or depression than in previous years.
These issues and others are discussed in detail in the relevant topic pages of this Users' Guide.
The following tables summarise the main differences in content between the 2011-12 and 2007-08 surveys:
SURVEY CONTENT POPULATION CHARACTERISTICS
|Topics covered ||2007-08 NHS ||2011-12 NHS ||Main items available from 2011-12 ||Comments on main differences between 2007-08 and 2011-12 |
|General demographics ||X ||X ||Sex; age; marital status (registered & social); Indigenous status; country of birth; year of arrival in Australia; main language spoken at home; proficiency in English; family type; household size, composition, type; geographic location. ||Same content in 2011-12 as in 2007-08|
|Education ||X ||X ||Highest year of school completed; whether has non-school qualification; level of highest non-school qualification; main field of study of non-qualification obtained; whether currently studying full or part time, location of current study||Same content in 2011-12 as in 2007-08. New items: main field and level of current study|
|Labour force ||X ||X ||Labour force status; status in employment; occupation, industry and industry sector of main job; hours worked; duration of unemployment; shift work ||Same content in 2011-12 as in 2007-08. New item: whether ever served in the Australian Defence Force |
|Income ||X ||X ||Personal gross weekly cash income; sources and main source; type of pension/benefit received; Household gross weekly cash income, equivalised; income deciles ||Same content in 2011-12 as in 2007-08|
|Housing ||X ||X ||Dwelling type; number of bedrooms; household tenure; landlord type||Same content in 2011-12 as in 2007-08. New items: whether has landline phone and whether number in white pages|
|Financial stress||X||Whether household members could raise $2000 in an emergency ||Not collected in 2007-08|
|Private health insurance/health cards ||X ||X ||Whether has PHI; type of cover; time covered by PHI; reasons having/not having PHI; duration with PHI; Whether has DVA or other Govt concession card: type of card ||Same content in 2011-12 as in 2007-08|
SURVEY CONTENT HEALTH CONDITIONS
|Topics covered ||2007-08 NHS||2011-12 NHS||Main items available from 2011-12 ||Main differences between 2007-08 and 2011-12 |
|Arthritis and Osteoporosis ||X ||X ||Type of arthritis; age first told arthritis; types of other specific actions taken for arthritis and osteoporosis; visits to health professionals; bone density checked and types of actions taken ||Similar content in 2011-12 to 2007-08. 2011-12 survey did not ask medication question specific to Arthritis and Osteoporosis, medication use was obtained from a separate module|
|Asthma ||X ||X ||Whether asthma worse or out of control; whether attended emergency; whether has written asthma action plan; visits to health professionals; and whether discussed self management; and types of actions taken ||Similar content in 2011-12 to 2007-08. 2011 - 12 survey did not ask medication question specific to asthma in the asthma module, medication use was obtained from a separate module|
|Cancer ||X ||X ||Cancer status; type of cancer; visits to health professionals; types of actions taken||Similar content in 2011-12 to 2007-08|
|Cause of reported long-term conditions ||X ||X ||Whether condition result of an injury; where injury occurred; age injury occurred ||Similar content in 2011-12 to 2007-08. New items: whether had food or drug allergies were specifically prompted for in 2011-12 and where identified, whether the allergy reaction was anaphylactic|
|Cardiovascular conditions ||X ||X ||Types of condition; blood pressure taken and by whom; cholesterol/blood pressure checks in last 12 months and 5 years and whether aspirin taken; types of actions taken ||Similar content in 2011-12 to 2007-08. 2011-12 survey did not ask medication question specific to cardiovascular conditions, medication use was obtained from a separate module|
|Diabetes/ high sugar levels ||X ||X ||Types of diabetes; type of other actions taken to manage condition; whether screened for diabetes in the last 3 years; age first told; whether condition interferes with usual activity; whether has diabetes-related sight problems; time since last visited optometrist/eye specialist; types of actions taken ||Similar content in 2011-12 to 2007-08. New items: Whether parents/siblings have been diagnosed with diabetes/high sugar levels|
|Disability ||X||X ||Disability status; type of disability; main type of disability. ||Similar content in 2011-12 to 2007-08. New items: assessment on the extent of disability|
|Kidney disease||X ||X ||Kidney disease status; use of dialysis; types of actions taken||Specific kidney disease module included in 2011-12; kidney disease status obtained from general long-term condition module in 2007-08|
|Long-term mental health condition ||X ||X ||Age diagnosed, number of times consulted health profession, use of common medications for mental health (e.g. sleeping tablets, antidepressants) and frequency/duration of use; types of actions taken. ||Similar content in 2011-12 to 2007-08; 2011-12 survey did not ask medication question specific to mental health, medication use was obtained from a separate module|
|Mental well-being ||X ||X ||Psychological distress (K10)||Same content in 2011-12 as 2007-08; 2011-12 survey did not ask medication question specific to mental health, medication use was obtained from a separate module|
|Bodily pain ||X ||X ||Bodily pain in last 4 weeks; whether interfered with work ||Same content in 2011-12 as 2007-08. 2011-12 asked 18+, 2007-08 asked 15+ |
|Self assessed health ||X ||X ||Self-assessed health ||Same content in 2011-12 as 2007-08|
|Status of condition ||X ||X ||Status for each condition reported ||Same content in 2011-12 as 2007-08. Slight wording changed to category 4 to include not diagnosed but long-term and current|
SURVEY CONTENT HEALTH RISK BEHAVIOURS
|Topics covered ||2007-08 NHS ||2011-12 NHS ||Main items available from 2011-12 ||Comments on main differences between 2007-08 and 2011-12 |
|Alcohol consumption ||X ||X ||Period since last drank; days consumed alcohol in last week; quantity of alcohol by type of drink consumed in last week (max 3 days); alcohol risk level; graduated frequency; how consumption changed since this time last year||Same content in 2011-12 as 2007-08. Questions on number of times respondent had 11, 7, 5, and 3 (new) standard drinks in a day in the last 12 months were broadened to be asked of all persons in 2011-12 to measure against 2009 single episode recommendations|
|Body mass ||X ||X ||Body mass index and measured height, weight and waist circumference measurements||Similar content in 2011-12 as 2007-08, except there were no self-reported measurements and no hip measurements|
|Dietary habits ||X ||X ||Type of milk usually consumed and fat content of milk; usual daily intake of vegetables & fruit and use of salt and whether it is iodised||Similar content to 2011-12 as 2007-08, with new questions for salt use |
|Exercise ||X ||X ||Type, frequency and duration of exercise in last week; exercise level; whether walked for transport; number of times walked, did moderate/vigorous exercises and total duration for each; time spent sitting at work and home on a usual work/week day ||Similar content in 2011-12 as 2007-08, except respondents are only asked about exercise in the last week rather than also in the last 2 weeks. |
|Smoking ||X ||X ||Smoker status; number of smokers in household, age started/stopped smoking regularly||Same content in 2011-12 as 2007-08|
|Family stressors||X||X||Family stressors in the last 12 months||Same content in 2011-12 as 2007-08. Referred to as Personal stressors in 2007-08|
|Breastfeeding ||X ||Whether was breastfed; age commenced and ended and whether fed other fluids including milk, formula, soy, juice, softdrink or water||Not collected in 2007-08. This topic is located in Health Related Actions in 2011-12.|