MethodIn this study , we use crosssectional data from surveys of adolescents and young adults conducted before 2010 , 2011 , 2012 and after 2013 the implementation of the tobacco plain packaging legislation to explore a range of responses to plain packaging of tobacco products . Data for this study come from the Tobacco Promotion Impact Study TPIS , conducted in the Australian states of New South Wales NSW and Queensland . The study had a repeat crosssectional design with yearly telephone surveys conducted in June of each year from 2010 to 2013 . The TPIS monitored adolescents ' and young adults ' 1224 years exposure to tobacco promotions , responses to tobacco control policies and smokingrelated cognitions and behaviours . Households were recruited using random digit dialling and participants within households were recruited using random selection selecting the nth oldest eligible person aged 1224 years . From 2010 to 2012 , recruitment was conducted using landline phone numbers only . In 2013 , because of concerns about the increasing proportion of Australian homes without a landline phone number from 17 % in 2010 to 22 % in 2012 , 31 a supplemental sample of youth was also recruited through random digit dialling to mobile phone numbers . The use of this supplemental sample is described below . Permission was obtained from parents of 1215 year olds before conducting interviews . Cooperation rates averaged 70 % among eligible respondents when taking into account households of unknown eligibility , response rates averaged 42 % American Association for Public Opinion Research Response Rate # 3 . 32 The TPIS was approved by the NSW Population and Health Services Research Ethics Committee . MeasuresSmoking status Respondents were asked if they had ever had a puff of a cigarette , how many cigarettes they had smoked in their lifetime , if they had smoked in the past month and whether they intended to smoke in the next 12 months . Based on staged models of smoking uptake and smoking susceptibility , 33 , 34 they were then classified as 1 never smokers never taken a puff 2 experimenters smoked 5 cigarettes ever , or smoked 5100 cigarettes in their lifetime but not in the past month 3 current smokers smoked in the past month , and smoked more than 5 cigarettes in their lifetime or 4 exsmokers smoked more than 100 cigarettes in their lifetime , but not in the past month . Never smokers were further classified into 1 nonsusceptible never smokers never taken a puff and certain they would not smoke in the next 12 months and 2 susceptible never smokers not certain that they would not smoke in the next 12 months . The number of exsmokers in each year was small therefore , experimenters and exsmokers were combined into one group in analyses reporting outcomes by year . Demographics Age , sex , state of residence and year of interview were included . The number of 1215 year olds among the samples of smokers , exsmokers and experimenters was small therefore , age was dichotomised 1217 vs 1824 years for analyses split by smoking status . Postcodes were used with the Socioeconomic Indices for Areas SEIFA 35 to indicate low quintiles 45 or moderatehigh quintiles 13 socioeconomic status SES . Respondents reported on the number of current smokers in their household and how many of their five closest friends smoked . Attitudes towards plain packaging All respondents were asked to indicate agreement with the statement ' I support regulation that ensures all tobacco products are sold in plain generic packaging ' 5 strongly disagree to 1 strongly agree . Responses were dichotomised to indicate support strongly agree and agree vs not and opposition strongly disagree and disagree vs not of plain packaging . 30 Responses to plain packaging Never smokers were asked ' What effect do you think the introduction of plain packaging will have on you ? Will it ' 20112012 or ' Has it ' 2013 1 made you more likely to try smoking 2 made you less likely to try smoking or 3 not influenced you . Exsmokers and experimenters who had not smoked in the past month were asked ' Will ithas it ' 1 made you more likely to smoke again 2 made you less likely to smoke again or 3 not influenced you . Current smokers were asked ' As a result of plain packaging , will you ' 20112012 or ' As a result of plain packaging , have you ' 2013 1 tried to quit 2 thought about quitting 3 hid your pack from view 4 felt embarrassed to be a smoker 5 used a case to cover your pack or 6 smoked more response optionsyesno . In 2013 , responses also included 7 changed brands and 8 smoked less . Statistical analysisSupport for and opposition to plain packaging by year of interview were investigated separately for current smokers , never smokers , experimenters and exsmokers . In order to determine if changes in attitudes from preimplementation to postimplementation were significant when controlling for changes in sample composition , we conducted logistic regression analyses predicting support and opposition . The independent variable was year of interview 2013 postimplementation , 20102012 preimplementation , and covariates included demographics age , sex , state , SES , smoking exposures number of friends and household members who smoke and cigarettes per day for the smoker sample . Logistic regression models were run to determine if nonsmoking youth never smokers and exsmokersexperimenters interviewed postimplementation were more likely to report that plain packaging made them less likely to smoke than those who anticipated this preimplementation . The independent variable in these models was year of interview , and covariates included demographics and smoking exposures . We also ran the logistic regression models predicting attitudes and responses to plain packaging in the subsample of susceptible never smokers in order to explore whether any changes over the years of the survey were apparent in the group of youth most at risk of smoking initiation . We investigated smokers ' responses to plain packaging by plotting the proportions of smokers who anticipated or reported each of the responses by year . In order to assess whether any differences in anticipated and actual responses were significant when controlling for sample variation , we conducted logistic regression analyses to predict 1 a quitrelated response thought about quitting or tried to quit 2 a social denormalisation response hid pack from view , felt embarrassed to be a smoker or used a case 3 smoking more or 4 no impact . The independent variable in these models was year of interview , and covariates included demographics , smoking exposures and cigarettes per day . We also conducted a sensitivity analysis in order to test if actual responses differed from anticipated responses even among smokers who were opposed to plain packaging , whereby we reran these four logistic regression models separately for smokers who opposed the regulations . Finally , in order to identify individual characteristics of youth who were , at postimplementation , more likely to support plain packaging or report a positive response , we ran a set of logistic regression analyses using the sample of youth interviewed in 2013 only . The outcomes investigated were support for plain packaging , less likely to smoke nonsmokers , quitting responses smokers and denormalisation responses smokers . Demographic and smoking characteristics were entered as the independent variables . The supplemental mobile phone sample was added in 2013 in order to assess whether any changes in outcomes between survey years were due to changes in the characteristics of the population covered by landlines . Previous studies have found that adding a mobile component to a landline population survey gives a more representative sample , 36 but that it also has the potential to result in changes to population estimates that are a consequence of the design change , rather than a real change . 37 Comparing the landlineonly and the dualframe landline and mobile samples to previous years allowed this issue to be explored . Therefore , all analyses comparing years of the survey were conducted twice . The first set of analyses used the dualframe sample for 2013 comparing differences between years while minimising the influence of the changing composition of a sample recruited via landline only . The second set of analyses used the landline sample only comparing differences between years while minimising the impact of the sampling change . The results reported in this paper will focus on the results from the first set of analyses using the dualframe sample for 2013 , with the landline results provided in an online supplementary table . Any differences in the pattern of results across the sampling frames are reported . The gender distribution of this sample was relatively consistent with population parameters as defined by Australian Bureau of Statistics ABS data . 35 There were , however , some discrepancies in the age distribution , particularly a slight overrepresentation of 1619 year olds , but underrepresentation of 2024 year olds . Given these discrepancies , data were weighted separately to the NSW and Queensland populations of 1224 year olds for age , sex and region distributions from Census data 35 using poststratification weights . In the set of analyses including the 2013 mobile phone supplement , additional weighting was used to account for telephony status landline only , mobilephone only or dualuser . All analyses were conducted using StataCorp , Stata V . 11 . 1 Texas , USA , 2009 .