Wilkinson et al. BMC Public Health 2012, 12:332 http://www.biomedcentral.com/1471-2458/12/332 family health history, and among women, reproductive history. After participants complete the survey, they are asked to provide biological samples. Finally height and weight are assessed using a standardized protocol. A total of 3,000 households with potential age-eligible (adolescents between the ages of 11 and 13 years) participants were identified from the cohort database. Of the first 1,425 potential participants’ parents or legal guardians contacted to assess interest in the study, just over 90% agreed to enroll their child in the study (N = 1,328). The institutional review board at The University of Texas M. D. Anderson Cancer Center approved all aspects of this study. Data collection After obtaining informed written consent, data were collected via personal interview in the home on two occasions: at baseline, when the participants were between the ages of 11 and 13 years, and roughly 30 months later, following identical procedures. Smoking-related constructs assessed at both home visits were identical. Items assessing physical activity and sensation seeking tendencies were included at the second home visit only. Given the focus of the current analysis, only participants who provided data at the second home visit are included in the current analysis, N = 1,154 or 87% of those enrolled at baseline. Thus participants in the current study were between the ages of 12 and 17 years when they completed the second home visit. Participants answered the survey either in English or Spanish on a hand held personal digital assistant (PDA) which enabled the participants to read the questions themselves and answer without their parents hearing or viewing their responses, thereby ensuring their privacy. Participants received a $25 gift card upon completion of the baseline and final home interviews. A detailed description of the baseline data collection procedures has been published elsewhere [23]. Measures All participants provided demographic information (gender, age, country of birth) when they enrolled at baseline. Female served as the reference category for gender. For country of birth – either Mexico or USA – born in Mexico served as the reference category. Age was entered as a continuous variable and reflected participants’ age at the second home visit. Household socio-economic status (SES) was controlled for using parental educational attainment rather than household income, both valid markers of SES, because more than 40% of the parents did not report their income, while the majority reported educational attainment. Parental educational attainment was divided into three categories: “less than high school,” “high school/General Educational Development equivalency” or “more than high Page 3 of 11 school,” with those with highest level of education serving as the reference category. For descriptive purposes, household income was divided into four categories: “less than $24,999 per year,” “$25,000-$44,999 per year,” “$45,000 or more,” and “missing.” Acculturation was assessed using four items that ascertain language used when reading, speaking at home, speaking with friends, and thinking [24]. Responses are made on a five-point scale ranging from “only Spanish” to “only English.” Based on our data, the scale has shown excellent internal reliability (alpha = 0.92). We created a three-level variable of acculturation with roughly equal numbers per level of acculturation based on the distribution of the data: Participants with a score of 3 or less were coded as “lowest acculturation,” those with a score above 3 and less than 4 were coded as “medium acculturation,” and those with a score of 4 or higher were coded as “highest acculturation.” Sensation seeking was assessed using a 26-item scale [25] from which three subscales were created, each with good internal reliability: thrill and adventure seeking (TAS; Cronbach’s alpha = 0.81), drug and alcohol attitudes (DAA; Cronbach’s alpha = 0.72) and social disinhibition (Cronbach’s alpha = 0.68). Participants endorse the choice that most describes what they like or feel, for example “a) I’d never do anything that’s dangerous” or “b) Sometimes I like to do things that are a little scary” is taken from the TAS scale; “a) I would like to try marijuana” or “b) I would never smoke marijuana” is taken from the DAA scale; and “a) I don’t like being around kids who act wild and crazy” or “b) I enjoy being around kids who sometimes act wild and crazy” is taken from the social disinhibition scale. Smoking behavior was assessed by: “Have you ever smoked a whole cigarette?” and “Have you ever tried a cigarette, even a puff?” A response of “yes” to either item indicated experimentation with cigarettes and was coded as “1” and a response of “no” to both was coded as “0.” Physical activity was assessed using the following two items, both of which were adapted from the Youth Risk Behavioral Surveillance System [26]: “Think about the activities you do at school, but not in PE. On how many days of the past 7 did you exercise or participate in physical activity for at least 60 minutes per day?” and “Think about activities you do in your community or at home. On how many days of the past 7 did you exercise or participate in physical activity for at least 60 minutes per day?” To facilitate comparisons between our sample and national samples [27], using both variables and regardless of context, participants who reported being physically active for at least 5 days were coded as “1,” which reflected meeting public health recommendations for physical activity for adolescents; and those who reported less physical activity were coded as “0,” which