Australia's Gambling Industries - Productivity Commission

Respondent selection method
A commonly used and recommended procedure for selecting individuals randomly
within households is some variant of the birthday approach — such as the individual
having the ‘nearest’ birthday or the ‘last’ birthday. For this survey, once a household
was contacted, the respondent was selected randomly as the adult (aged 18 years or
older) normally living in the household who had the last birthday.
As advised by some of the survey consultants approached by the Commission, while
the last birthday method is a rigorous method of respondent selection, it can have a
limitation. If used on its own, without sufficient callbacks, it can result in an
undersampling of younger people and an oversampling of older people, because
younger people (especially younger males) are more often ‘not at home’ and
therefore more difficult to contact. It is therefore important that survey protocols
using the last birthday method also allow for a sufficiently large number of
callbacks.
One survey consultant (ACNielsen) noted that with a last birthday selection method,
there will inevitably be some under-representation of young males, but that:
In any case, the distortion can be corrected [by] age/gender weighting ... and while the
extent of the need to correct a distortion with weighting will impact in terms of
increasing the sampling error of any estimates from the sample, it is arguable that this
increase in sampling error is still appreciably less than the increase in non-sampling
error that comes from the non-response bias inherent in quota sampling systems
(personal communication).
ACNielsen also argued that from its experience, the last birthday method is
preferable to alternatives such as Kish-grid type selection methods:
... over a series of tests we conducted ... we found that anything approaching a Kishtype
grid, or a last birthday method which started with asking the number of people in
the household was ultimately unproductive, as refusals and mid-screening terminations
increased, and overall the process slowed down interviewing significantly (personal
communication).
F.7 Quotas and weighting
While the last birthday method of respondent selection coupled with an adequate
number of callbacks should generate a sample that is generally random and
representative, it is still likely that adjustments will be needed either by the use of
quotas, or weighting or both. This study used an approach of:
• having ‘strict’ quotas based on area (by state/territory and metropolitan/country),
and ‘loose’ quotas based on age and gender; and
F.20 GAMBLING