Australia's Gambling Industries - Productivity Commission

ecause of non-payment), while there are telephone number selection methods that
can be used to minimise the latter problem.
Household selection method
Three alternative methods were considered for drawing the sampling frame for
telephone interviewing:
• randomly from residential telephone numbers in the latest electronic White Pages
directory (RWP);
• using random digit dialling (RDD); or
• using an adaptation of random digit dialling (MRDD) — such as selecting
residential telephone numbers at random from the White Pages directory and
incrementing the last digit by one (to get unlisted or not yet listed numbers).
There are advantages and disadvantages associated with each approach.
RWP has the highest proportion of usable contacts, because the number of
telephone numbers dialled that turn out to be faxes or businesses or out of service is
lower than for either RDD or MRDD. But it has two main disadvantages:
• individuals with silent (unlisted) numbers are excluded from the listings; and
• individuals who have only recently moved or been connected are excluded.
The advantages of RDD arise precisely in these two areas: it throws up silent
numbers and it can capture recent movers. But it also has disadvantages:
• it produces a much higher level of unusable numbers than RWP — even RDD
systems which automatically cross check the sample with the Yellow Pages
cannot avoid selecting numbers which are either faxes, not in use or unlisted
business numbers; and
• contacting unlisted numbers is not necessarily an advantage — individuals who
have a silent number have signalled that they do not wish to be annoyed by
unsolicited calls, and hence there is a much greater likelihood of refusal.
Modified RDD lies somewhere in between — it tends to generate fewer non-usable
numbers than RDD, but still much greater than RWP. So more dialling is required
than for RWP, which yields a higher proportion of possible contacts.
Overall, while RDD reduces several sources of bias inherent in RWP (unlisted
numbers and recent movers), it does so at higher cost and with greater likelihood of
more refusals. So on balance, the Commission opted for the RWP approach.
NATIONAL GAMBLING
SURVEY
F.19