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METHODOLOGY

• The 2015 CTASS was administered by the Social Research Centre (SRC) on behalf of the Australian Bureau of Statistics (ABS) and involved two surveys conducted via Computer Assisted Telephone Interviewing (CATI): a survey of the general community and of informed users of ABS statistics.
• The questionnaires were modified from the 2010 questionnaires by the ABS with consideration given to maintaining comparability with the 2010 surveys. SRC reviewed the questionnaires and provided recommendations based on recent best practice and available concordances and population benchmarks.
• The research was undertaken in accordance with the Privacy Act (1988) and the Australian Privacy Principles contained therein, the Privacy (Market and Social Research) Code 2014, the Australian Market and Social Research Society’s Code of Professional Practice, and ISO 20252 standards.

• The 2015 CTASS design entailed the conduct of 2,200 interviews with Australians aged 15 years and over. A dual-frame (using both landline and mobile numbers) sample frame was used. The blend of mobile phone interviews was 50%.
• The randomly generated sample lists were purchased from SamplePages, one of the two main vendors supplying samples to the market and social research industry in Australia.
• For the landline sample, a ‘best estimate’ of postcode is assigned to each record at the number generation and testing stage, based on information available about the geographic area serviced by each individual telephone exchange. Therefore, to ensure a nationally representative sample, random sampling was conducted within 15 geographic strata (State / Territory, Capital City / Rest of State).
• For the mobile phone sample, phone numbers were generated and tested based on the known mobile phone number prefixes. No geographic information is currently available to researchers for mobile phone numbers generated in this way, therefore, the mobile sample was drawn as one sample strata.
• A summary of the distribution of interviews is presented in Table 13.

Strata	Region	QUOTA
		n	%
Landline
1	Sydney	227	10.3
2	Rest of NSW	128	5.8
3	Melbourne	209	9.5
4	Rest of VIC	69	3.1
5	Brisbane	106	4.8
6	Rest of QLD	112	5.1
7	Adelaide	64	2.9
8	Rest of SA	20	0.9
9	Perth	88	4.0
10	Rest of WA	24	1.1
11	Hobart	11	0.5
12	Rest of TAS	13	0.6
13	Darwin	7	0.3
14	Rest of NT	4	0.2
15	ACT	18	0.8
Mobile
16	Mobile	1 100	50.0
Total
	All respondents	2 200	100

• For within-household respondent selection of the landline sample, a next birthday method of selection was used in 50% of cases and a modified Westat selection process in the remainder.
• As detailed in Table 14, a total of 69,108 calls were placed during June and July 2015 to a sample pool of 18,509 sample records to achieve 2,200 survey interviews. The co-operation rate for the survey (total interviews completed of the total number of interviews and refusals) was 61%. Non-response analysis was conducted and weighting applied to correct for variations between respondents and non-respondents.
• The general community survey recorded an average interview length of 13.3 minutes.

• To ensure estimates made from the general community survey were representative of Australians aged 15 years or older, weights were calculated for each respondent in the dataset. Initial weights were calculated as the inverse of the product of the probability of selection (accounting for the overlapping mobile and landline populations) and of the probability of response (based on a regression model incorporating auxiliary data available for both respondents and non-respondents). The initial weights were then adjusted so that they satisfied population benchmarks for age, gender, state, education, country of birth, and telephone status.
• For comparison with the 2010 CTASS results, it was necessary to obtain a dual-frame estimate for the 2010 survey, given that only a landline estimate was available in 2010 (as the sample frame at that time was the Electronic White Pages and mobile numbers were not included in the sample). The ABS therefore developed a weighting strategy to allow for the calculation of a dual-frame estimate. The efficacy of the adjustments relies heavily on the assumptions of “constant proportionality” between landline and mobile phone responses. As these assumptions cannot be tested, time series results presented in this report should therefore be treated as indicative only.
• Statistical significance testing was conducted using the well-known Kish approximations (IBM, 2011; Kish, 1965; Potthoff et al, 1992)¹. Caution should be used when drawing conclusions about reported significant differences for sub-groups where the effective sample size is not an adequate representation.
• Subgroup categories (for example male and female for gender) were derived from sample details (such as state for the landline sample) or questions asked in the survey. The one exception was socio-economic status (SES) which was derived from the education and occupation questions asked in the survey with concordance to data available from the Australian Council for Educational Research (ACER)².

• The informed users survey set out to complete around 140 interviews from a list of 191 users of ABS statistics (see Table 15). The list comprised of three different sample types: academics, economists and journalists. No quotas were set by sample type, however, additional attempts were made to maximise responses from the two smallest sample groups, economists and journalists.
• The final numbers achieved within sample groups were reflective of the sampling approach applied to each. As such, journalists and academics, who had consented to participating in the survey after receiving prior notification from the ABS, recording higher participation rates than economists who were approached cold.

	Sample records provided	Interviews achieved	Proportion of sample
Type	No.	No.	No.
Academic	163	131	80
Journalist	2	2	100
Economist	26	9	35
Total	191	142	74

• As detailed in Table 16, a total 553 calls were placed to achieve 142 survey interviews. The co-operation rate for the survey was 99%. The informed users survey recorded an average interview length of 13.1 minutes.

• For reporting purposes, the two smallest user groups (economists, n=9; and journalists, n=2) have been combined to protect the privacy of the smallest group and to ensure their individual responses are not identifiable. Weighting was not applied to the informed users data.