Australia's Gambling Industries - Productivity Commission

particular area/age/gender cell from the screener, then in effect only the fourth
would have been interviewed (a sampling ratio of 1 in 7) whereas if there had been
eight then the eighth would also have been interviewed (and the sampling ratio
would have been 1 in 4). For each cell, adjustment factors reflecting the specific
sampling ratios were calculated for non gamblers and non-regulars, so that no biases
are introduced from the random interview strategy.
As with the phase 1 screener weights, the phase 2 weights sum to the total number
of adults in the Australian population in 1997-98 (14.126 million).
F.8 Other survey protocols
Protocols were put in place in the National Gambling Survey to maximise the
contact rate and minimise non-response (refusals).
Procedures for maximising the contact rate
The following procedures were used with the aim of achieving as high a contact rate
as possible:
• generally calling in the evening or at weekends when individuals were more
likely to be at home;
• allowing the phone to ring at least 10 times before hanging up;
• making up to 4 callbacks (that is, 5 contact attempts) to achieve an initial contact
— most survey research shows that the impact on contact rates is minimal after
this number of attempts (see Steel, Vella and Harrington 1996);
• allowing a further 5 callbacks to achieve an interview, once contact was made
and a respondent identified;
• varying the time of day and day of week for callbacks, to increase the chance of
catching gamblers who might be out during the evening; and
• allowing a fieldwork phase of sufficient duration to ensure that the proportion of
numbers dialled that did not have their full number of callbacks completed was
minimal.
Procedures for maximising the respondent participation rate
Another important consideration was to have protocols in place to maximise the
participation rate once a respondent was contacted. This included:
• wording the introduction to the survey to encourage participation by stressing:
NATIONAL GAMBLING
SURVEY
F.23