• The National Drug Strategy Household Survey (NDSHS) provides three-yearly estimates of the proportion of the population aged 12 years and older using tobacco, alcohol and illicit drugs. The Survey also captures information about drug-related attitudes, perceptions and support for government policy.
• It is known from past studies of alcohol and tobacco consumption that respondents tend to underestimate actual consumption levels.
• Estimates of illicit drug use and related behaviours are also likely to be underestimates of actual practice.
• Reported findings are based on self-reported data and are not empirically verified by blood tests or other screening measures.
• The response rate for the 2010 survey was 50.6%.  Given the nature of the topics in this survey, some non-response bias is expected, but this bias has not been measured.
• Both sampling and non-sampling errors should be considered when interpreting results.
  

Published results from the 2010 NDSHS are available on the AIHW website see 2010 National Drug Strategy Household Survey report.

Users can request data not available online or in reports via the Communications, Media and Marketing Unit on (02) 6244 1032 or via email to [email protected]. Requests that take longer than half an hour to compile are charged for on a cost-recovery basis.

A confidentialised unit record file is available for 3rd party analysis through the Australian Data Archive. Access to the master unit record file may be requested through the AIHW Ethics Committee.

Scope and coverage
The NDSHS collects self-reported information on tobacco, alcohol and illicit drug use and attitudes from persons aged 12 years and over.

Excluded from sampling were non-private dwellings (hotels, motels, boarding houses, etc.) and institutional settings (hospitals, nursing homes, other clinical settings such as drug and alcohol rehabilitation centres, prisons, military establishments and university halls of residence). Homeless persons were also excluded as well as the territories of Jervis Bay, Christmas Island and Cocos Island.

The exclusion of people from non-private dwellings and institutional settings, and the difficulty in reaching marginalised people are likely to have affected estimates.

The 2010 NDSHS was designed to provide reliable estimates at the national level. The survey was not specifically designed to obtain reliable national estimates for Aboriginal and Torres Strait Islander people, as there was no target sample size for Indigenous Australians. In 2010, the sample size for Indigenous Australians was smaller than anticipated based on population estimates, and so estimates based on this population group should be interpreted with caution.

Reference period
The fieldwork was conducted from 29 April to 14 September 2010. Respondents to the survey were asked questions relating to their beliefs and experiences covering differing time periods, predominantly over the previous 12 months.

Geographic detail
In 2010, data were coded to the census collector’s district level. Data are generally published at the national level with a selection of data published at the State/Territory and Remoteness Area levels.

Statistical standards
Data on tobacco and alcohol consumption were collected in accordance with World Health Organization standards and alcohol risk data were reported in accordance with the current 2009 National Health and Medical Research Council’s ‘Australian Guidelines to Reduce Health Risks from Drinking Alcohol’.

Australian and New Zealand Standard Classification of Occupations (ANZSCO) and Australian and New Zealand Standard Industry Classification (ANZSIC) codes were used as the code-frame for questions relating to occupation and industry. 

Type of estimates available
Unadjusted estimates of drug use prevalence, attitudes and beliefs are most commonly reported. In addition, some population estimates and age-standardised data are available for some aspects of the collection. Time series data are also presented for most estimates in the 2010 NDSHS report.

Perceptions of behaviour
It is known from past studies of alcohol and tobacco consumption that respondents tend to underestimate actual consumption levels (Stockwell et al. 2004). There are no equivalent data on the tendencies for under- or over-reporting of actual illicit drug use.

However, illicit drug users, by definition, have committed illegal acts. They are, in part, marginalised and difficult to reach. Accordingly, estimates of illicit drug use and related behaviours are likely to be underestimates of actual practice.

Sample design
The sample was stratified by region (15 strata in total ─ capital city and rest of state for each state and territory, with the exception of the Australian Capital Territory, which operated as one stratum). To produce reliable estimates for the smaller states and territories, sample sizes were boosted in Tasmania, the Australian Capital Territory and the Northern Territory. An additional 1,200 booster sample was also allocated to Queensland.

The over-sampling of lesser populated states and territories produced a sample that was not proportional to the state/territory distribution of the Australian population aged 12 years or older. Weighting was applied to adjust for imbalances arising from execution of the sampling and differential response rates, and to ensure that the results relate to the Australian population.

Sampling error
The measure used to indicate reliability of individual estimates reported in 2010 was the relative standard error (RSE). Only estimates with RSEs of less than 25% are considered sufficiently reliable for most purposes. Results subject to RSEs of between 25% and 50% should be considered with caution and those with relative standard errors greater than 50% should be considered as unreliable for most practical purposes.

Non-sampling error
In addition to sampling errors, the estimates are subject to non-sampling errors. These can arise from errors in reporting of responses (for example, failure of respondents’ memories, incorrect completion of the survey form), the unwillingness of respondents to reveal their true responses and the higher levels of non-response from certain subgroups of the population.

Reported findings are based on self-reported data and not empirically verified by blood tests or other screening measures.

Response rates and contact rates
Overall, contact was made with 52,690 in-scope households, of which 26,648 questionnaires were categorised as being complete and useable, representing a response rate for the 2010 survey of 50.6%, slightly lower than the drop and collect component of the 2007 survey (51.6%).
Some survey respondents did not answer all questions, either because they were unable or unwilling to provide a response. The survey responses for these people were retained in the sample, and the missing values were recorded as not answered. No attempt was made to deduce or impute these missing values.

A low response rate does not necessarily mean that the results are biased. As long as the non-respondents are not systematically different in terms of how they would have answered the questions, there is no bias. Given the nature of the topics in this survey, some non-response bias is expected. If non-response bias in the NDSHS is to be eliminated as far as possible, there would need to be additional work conducted to investigate the demographic profile of the non-respondents and the answers they may have given had they chosen to respond.

Indigenous Data
The survey was not specifically designed to obtain reliable national estimates for Aboriginal and Torres Strait Islander people, as there was no target sample size for Indigenous Australians. In 2010, the sample size for Indigenous Australians was smaller than anticipated based on population estimates, and so estimates based on this population group should be interpreted with caution.
For more information on the limitations of the survey results see Chapter 14 of the 2010 NDSHS report ‘Explanatory notes’.

Surveys in this series commenced in 1985. Over time, modifications have been made to the survey’s methodology and questionnaire design. The 2010 survey differs from previous versions of the survey in several respects, relating to data collection methodology and some of the questions asked.

Methodology
The 2010 survey was the first to exclusively use the drop and collect method. In 2007 and 2004, a combination of computer-assisted telephone interviews (CATI) and drop and collect methods were used, and in earlier waves, personal interviews were also conducted.

The change in methodology in 2010 does have some impact on time series data, and users should exercise some degree of caution when comparing data over time.

Fieldwork was conducted between April and September 2010, slightly earlier than in previous waves.

Sample
To produce reliable estimates for the smaller states and territories, sample sizes were boosted in Tasmania, the Australian Capital Territory and the Northern Territory. An additional 1,200 booster sample was also allocated to Queensland.

In 2010, to improve the geographic coverage of the survey, interviewers were flown to Very remote areas selected in the sample. In previous surveys, some Very remote areas that were initially selected in the sample would have been deemed inaccessible and not included in the final sample.

Questionnaire
The 2010 questionnaire was modelled on the 2007 version, to maintain maximum comparability. However, some refinements were made to ensure the questions remained relevant and useful. For more information on questionnaire changes in 2010 see Chapter 14 of the 2010 NDSHS report ‘Explanatory notes’.

Comparison with other collections
Comparisons of data from previous waves of the NDSHS, the National Health Survey and the Australian School Student’s Alcohol and other Drug Survey show variations in estimates. Differences in scope, collection methodology and design may account for this variation and comparisons between collections should be made with caution.