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BENCHMARKS, WEIGHTING AND ESTIMATION
Weighting is the process of adjusting results from a sample survey to infer results for the total in scope population whether that be persons, income units or households. To do this, a 'weight' is allocated to each sample unit e.g., a person or a household. The weight is a value which indicates how many population units are represented by the sample unit. The first step in calculating weights for each unit is to assign an initial weight, which is the inverse of the probability of being selected in the survey. For example, if the probability of a household being selected in the survey was one in 600, then the household would have an initial weight of 600 (that is, it represents 600 households).
An adjustment is then made to the initial weights to ensure that seasonal variation is appropriately represented in the survey estimates. After this initial adjustment, the sum of the weights of households in each quarter is in proportion to the length of the quarter (which align across the financial year with pension indexation dates rather than calendar quarter).
The initial weights are then calibrated to align with independent estimates of the population of interest, referred to as 'benchmarks'. Weights calibrated against population benchmarks ensure that the survey estimates conform to the independently estimated distribution of the population rather than to the distribution within the sample itself.
Most of the independent person and household benchmarks are based on demography estimates of numbers of persons and households in Australia. The benchmarks are adjusted to include persons and households residing in private dwellings only and to exclude persons living in very remote areas, and therefore do not, and are not intended to, match estimates of the Australian resident population published in other ABS publications. The demography estimates of persons (estimated resident population - ERP) and households used in HECS are built up from the 2006 Census.
In the HECS, each household, and all persons in each household were assigned a weight. Weighting was not performed for responses to the longitudinal component of HECS.
The benchmarks used in the calibration of the final weights for the HECS were:
Estimates produced from the HECS are usually in the form of averages (e.g. average energy expenditure of couple households with dependent children), or counts (e.g. total number of households that use particular sources of energy). For counts of households, the estimate was obtained by summing the weights for the responding households in the required group (e.g. those owning their own dwelling). For counts of persons, the household weights were multiplied by the number of persons in the household before summing. The HECS collects data on the number of people, including children, in each household but separate records with income and other detailed data were only collected for people aged 15 years and older.
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