The ABS have developed an approach that will achieve efficiencies in field work for social surveys while maintaining data quality.
Enumerating a national household survey with the same sample spread over several years rather than in a single year allows flexibility in statistical outputs, including more timely publication of some estimates. However, this can lead to increased collection costs if the sample in each year is broadly dispersed geographically. Essentially this is equivalent to running several national surveys with small samples and, due to the interviewer and travel costs, the collection cost per responding household is higher than if the full survey had been conducted in a single year.
If sample in a particular area can be enumerated within the same year, these costs can be reduced significantly as the recruitment, training and management of an interviewer for that area only needs to be done once, not repeatedly for multiple years. Travel from the interviewers' homes to sampled areas can also be done in fewer journeys, rather than returning to nearby areas in multiple years.
After considering several alternatives, we chose an approach that ensures that selected sample that lies in the same SA4 (as defined in the Australian Statistical Geography Standard) is enumerated in the same year. To achieve this, we group all of the SA4s in the country into segments and select a sample from a different segment each year. By defining the segments as groups of pre-defined geographical areas, we are able to select sample each year using the most up to date sample frame available. We have designed the segments to be balanced (with respect to some key data items) in a way that ensures samples each year are selected from a segment that is nationally representative. We also balance the segments for states and parts-of-state (metropolitan and rest of state). This requires grouping SA3s rather than SA4s in some parts-of-state that have a small number of SA4s. The effective balancing of segments to ensure they are representative nationally has been confirmed by analysis of past survey data and Census data.
This method has been reviewed from practical and theoretical perspectives by internal and external advisory bodies. This advice has helped us to develop suitable selection and estimation methods, giving us confidence that this approach will give substantial efficiency gains in the field while maintaining data quality.
For more information, please contact Alex Stuckey Methodology@abs.gov.au