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 4363.0.55.001 - Australian Health Survey: Users' Guide, 2011-13   Latest ISSUE Released at 11:30 AM (CANBERRA TIME) 07/12/2012
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Contents >> Survey design and operation >> Weighting, benchmarking and estimation procedures

WEIGHTING, BENCHMARKS AND ESTIMATION PROCEDURES

Weighting

Weighting is the process of adjusting results from a sample survey to infer results for the total in-scope population. To do this, a 'weight' is allocated to each sample unit; that is, a person or a household. The weight is a value which indicates how many population units are represented by the sample unit. Separate person and household weights were calculated, as only one adult and one child per household were enumerated. The steps used to derive person and household weights are described below.

Initial household weight

The first step of the weighting procedure was to assign an initial household weight to fully responding dwellings. The initial household weight was calculated as the inverse of the probability of the household's selection in the sample. For example, if the probability of a household being selected in the survey was 1 in 600, then the household would have an initial weight of 600 (that is, it represents 600 households).

The initial household weight was then adjusted as described below.

Initial person weights

After obtaining adjusted initial household weights, initial weights were assigned to fully-responding persons based on the sub-sampling scheme deployed within households. Initial person weights were calculated by multiplying the person's household weight by the probability of the person being selected. For persons 18 years and over, the household weight was multiplied by the number of adults aged 18 years and over in the household, and for persons 0-17 years old, the household weight was multiplied by the number of children, of selected age applicable to the survey, in the household.

In developing the survey weights, information available for responding and non-responding households was used to conduct quantitative investigations into explicit non-response adjustments. No explicit non-response adjustment was made to the weighting however, as the effect of the investigated non-response adjustments to the estimates was negligible.

Benchmarks

Person and household weights are calibrated to independent estimates of the population of interest, referred to as 'benchmarks'. Weights calibrated against population benchmarks ensure that the survey estimates conform to independently estimated distributions of the population rather than to the distribution within the sample itself. Calibration to benchmarks helps to compensate for over- or under-enumeration of particular categories of persons and households, which may occur due to the random nature of sampling or non-response.

The NHS was benchmarked to the estimated resident population living in private dwellings in non-Very Remote areas of Australia at 31 October 2011, based on the 2006 Census of Population and Housing. Excluded from these benchmarks were persons living in discrete Aboriginal and Torres Strait Islander communities, as well as a small number of persons living within Collection Districts that include Aboriginal and Torres Strait Islander communities. The benchmarks and hence the estimates from the survey do not (and are not intended to) match estimates of the total Australian estimated resident population (which include persons living in Very Remote areas of Australia and persons in non-private dwellings) obtained from other sources.

Calibration to household level benchmarks

The household benchmarks used in the 2011-12 NHS weighting were preliminary household estimates for 31 October 2011, based on the 2006 Census of Population and Housing, scoped to the NHS.

The calibration levels used for benchmarking were State by Part of State by household composition (numbers of persons 0-14 years old, numbers of persons 15 years and over).

Calibration to person level benchmarks

The person benchmarks used in the 2011-12 NHS were preliminary population estimates for 31 October 2011 based on the 2006 Census of Population and Housing, scoped to the NHS.

The calibration levels used for benchmarking were State by Part of State by sex by age group (0-1 years, 2-4 years, 5-9 years, 10-11 years, 12-14 years, 15-17 years, 18-24 years, 25-29 years, 30-34 years, etc., 70-74 years, 75 years and over).

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