Efforts were made to minimise non-sampling error by careful design and testing of questionnaires, intensive training of interviewers, and extensive editing and quality control procedures at all stages of data processing. However, errors can be made in giving and recording information during an interview. These types of inaccuracies are referred to as non-sampling errors and include errors in the survey scope, response errors, processing errors and bias due to non-response.
As the response rate for this survey was lower than expected (60%), extensive non-response analyses were undertaken to assess the reliability of the survey estimates. As a result, adjustments were made to the weighting strategy. As non-response can vary across population characteristics, as well as across data items, users should exercise caution. Detailed information on survey methodology and non-response is provided in the Users' Guide.