Abstract
BackgroundIn Australia telephone surveys have been the method of choice for ongoing jurisdictional population health surveys. Although it was estimated in 2011 that nearly 20% of the Australian population were mobile-only phone users, the inclusion of mobile phone numbers into these existing landline population health surveys has not occurred. This paper describes the methods used for the inclusion of mobile phone numbers into an existing ongoing landline random digit dialling (RDD) health survey in an Australian state, the New South Wales Population Health Survey (NSWPHS). This paper also compares the call outcomes, costs and the representativeness of the resultant sample to that of the previous landline sample.MethodsAfter examining several mobile phone pilot studies conducted in Australia and possible sample designs (screening dual-frame and overlapping dual-frame), mobile phone numbers were included into the NSWPHS using an overlapping dual-frame design. Data collection was consistent, where possible, with the previous years’ landline RDD phone surveys and between frames. Survey operational data for the frames were compared and combined. Demographic information from the interview data for mobile-only phone users, both, and total were compared to the landline frame using χ2 tests. Demographic information for each frame, landline and the mobile-only (equivalent to a screening dual frame design), and the frames combined (with appropriate overlap adjustment) were compared to the NSW demographic profile from the 2011 census using χ2 tests.ResultsIn the first quarter of 2012, 3395 interviews were completed with 2171 respondents (63.9%) from the landline frame (17.6% landline only) and 1224 (36.1%) from the mobile frame (25.8% mobile only). Overall combined response, contact and cooperation rates were 33.1%, 65.1% and 72.2% respectively. As expected from previous research, the demographic profile of the mobile-only phone respondents differed most (more that were young, males, Aboriginal and Torres Strait Islanders, overseas born and single) compared to the landline frame responders. The profile of respondents from the two frames combined, with overlap adjustment, was most similar to the latest New South Wales (NSW) population profile.ConclusionsThe inclusion of the mobile phone numbers, through an overlapping dual-frame design, did not impact negatively on response rates or data collection, and although costing more the design was still cost-effective because of the additional interviews that were conducted with young people, Aboriginal and Torres Strait Islanders and people who were born overseas resulting in a more representative overall sample.
Highlights
In Australia telephone surveys have been the method of choice for ongoing jurisdictional population health surveys
There is substantial international literature on conducting random digit dialling (RDD) surveys with mobile phone augmentation [8,9,10,11,12] and the American Association for Public Opinion Researchers (AAPOR) Cell Phone Task Force recommended in their latest report (2010) [12]: “Random digit dialling (RDD) surveys without cell phone augmentation should in their methods report how they have produced unbiased estimates without the cell phone only segment”
This paper describes the methods used for the inclusion of mobile phone numbers into the New South Wales Population Health Survey (NSWPHS), an existing ongoing landline RDD health survey in an Australian state [13]
Summary
In Australia telephone surveys have been the method of choice for ongoing jurisdictional population health surveys It was estimated in 2011 that nearly 20% of the Australian population were mobile-only phone users, the inclusion of mobile phone numbers into these existing landline population health surveys has not occurred. This paper describes the methods used for the inclusion of mobile phone numbers into an existing ongoing landline random digit dialling (RDD) health survey in an Australian state, the New South Wales Population Health Survey (NSWPHS). Because of increasing numbers of mobile-only phone users worldwide, currently estimated to be 30.2% in the USA [1], 13% in Canada [2], 14% - 19% across the UK countries [3] and 19% in Australia [4], it has become increasingly difficult to produce unbiased estimates from random digit dialling (RDD) surveys that only target landline phones [5,6,7]. The overlapping dual-frame design, requiring a more complex weighting strategy, has been growing in favour because it has been shown that persons selected through mobile frames (even if they have both mobile and landline phones) differ to persons selected through landline frames [7]
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