Australia's Gambling Industries - Productivity Commission

• post-weighting the sample data for phase 1 (screener questionnaire) and phase 2
(full interview) respondents.
Quotas
The strict quotas for completed screener interviews based on area are those set out
in table F.2. Approximate rather than strict age and gender quotas were used to
ensure sufficient representation of each age/gender group, as a compromise solution
to survey accuracy and cost. This involved setting minimum and maximum bounds
(of ±33 per cent) around the strict quotas, and monitoring the degree to which the
quotas were being met as the survey proceeded. Such an approach means that
modest differences between each age/gender/area cell size in comparison with those
that would apply with strict quotas are acceptable, bringing about a major reduction
in the cost of the survey but only a small reduction in accuracy. The deviations from
ABS age/gender/area population data are then corrected by applying weights to the
sample data.
In relation to the ‘loose’ quotas, it became apparent towards the end of the fieldwork
phase that some of the minimum age/gender quotas would not be met in some of the
smaller States. Hence, in place of the last birthday method — which was used to
complete 10 365 interviews — the approach taken was to ask to speak to the
youngest male aged 18 or older (and then the youngest female) before substituting
for another adult within the household. This enabled all minimum quotas to be met,
but the number of screener interviews needed to be completed slightly exceeded the
original 10 500 — 10 609 participants completed the screener.
Weighting schemes for population estimates
Information for the sample respondents was multiplied by weighting factors to
provide estimates for the whole population. Because of the selective (random)
interview strategy used in phase 2 of the questionnaire, separate weights are
appropriate for the screener respondents and the full interview respondents.
Phase 1 weights — Screener respondents
As noted in section F.5, the sample was stratified across 120 area/age/gender cells.
The weight for each screener respondent in a given cell was calculated as:
WTSCR = (HHSize) * [cell population / ΣHHSize].
NATIONAL GAMBLING
SURVEY
F.21