Int. J. Environ. Res. Public Health 2011, 8 414 Institute (USA), the University of Illinois at Chicago (USA), the University of Stirling (UK), the University of Nottingham (UK), and the Cancer Council Victoria (Australia). 2.1. Participants Selected participants included 8,245 current and former adult smokers who were interviewed as part of Wave 5 of the ITC-4 survey between October 2006 and February 2007 (Canada, n = 2,023; the US, n = 2,034; the UK, n = 2,019; and Australia, n = 2,169). Between September 2007 and February 2008, a total of 5,866 of these participants (71.1%) were successfully re-interviewed in Wave 6 (Canada, n = 1,459, 72.1%; the US, n = 1,291, 63.5%; the UK, n = 1,484, 73.5%; and Australia, n = 1,632, 75.2%). In addition, another 2,329 individuals were recruited as part of the Wave 6 replenishment sample (Canada, n = 556; the US, n = 711; the UK, n = 523; and Australia, n = 539). 2.2. Measures 2.2.1. Socioeconomic status Questions related to respondent education and annual household income were used to create previously utilized indices of self-reported socioeconomic status [14,15]. Respondents were categorized into three levels of educational attainment: low (less than high school diploma), moderate (high school diploma), and high (some university training or a university degree). Similarly, respondents from the US, Canada, and Australia were categorized into three levels of annual household income: low ($29,999 or less), moderate ($30,000 to $59,999), and high ($60,000 or more). In an effort to account for variation in currency values, respondents from the UK were categorized into annual household income categories using a modified rubric: low (£15,000 or less), moderate (£15,001 to £30,000), and high (£30,001 or more). These education and income categories were then combined to create a previously utilized composite measure for SES [33] as follows: low (low education and low income), moderate (low income and moderate education, low income and high education, moderate income and low education, and high income and low education), and high (moderate income and moderate education, moderate income and high education, high income and moderate education, and high income and high education). Respondents who did not report either income (5.7%) or education (0.3%) were excluded from the analysis. The aforementioned categorization methods resulted in a similar distribution across countries and tertile divisions. 2.2.2. Smoke-Free policy presence, introduction, retention, and removal The presence of a smoke-free home policy was assessed using the question, ‘Which of the following best describes smoking in your home?’, with the following response options: ‘smoking is allowed anywhere in your home’, ‘smoking is never allowed anywhere in your home’, or ‘something in between’. A respondent was considered to be covered by a total ban in their home if they answered ‘smoking is never allowed anywhere in your home’ and a partial ban if they answered ‘something in between’. The presence of a smoke-free bar policy was assessed using the question, ‘Which of the following best describes the rules about smoking in drinking establishments, bars, and pubs where you live?’,