e., ��decline to answer��) responses to self-report instruments included in the analyses were imputed using best-set regression (StataCorp, 2009). All variables had less than 5% of data imputed. A variable reflecting never the number of imputed variables for each participant was included in all multivariate models to adjust for the impact that imputation may have had on the results. Statistical Analyses Baseline characteristics of participants were compared by the study arm using chi-square or t tests depending on the measurement��s scale. Logistic regression models were used to estimate the odds of quitting for the intervention versus control groups.

Analyses were conducted in two ways: intent-to-treat (ITT) such that all randomized individuals were included in the analysis (all participants lost to follow-up were assumed to still be smoking) and per-protocol analysis such that only those who completed the follow-up measures were included in the analysis. Models were adjusted for additional factors that may influence smoking outcomes in this population (denoted as ��aOR�� for adjusted odds ratio). Because of their influence on cessation rates (Centers for Disease Control and Prevention, 2001; Nordstrom et al., 2000), biological sex and baseline intensity of smoking were examined as effect modifiers. Given the study��s outreach focus to enroll young adults outside of higher education settings and those of minority race, these characteristics also were tested for effect modification. RESULTS As shown in Figure 1, 1,916 people expressed interest in participating, 585 (31%) of whom appeared eligible based upon the online screener form.

Of these 585, contact was not made with 49% (n = 284). Fifteen percent (n = 90) declined to participate: reasons included the incentives being too low and not having enough time to engage with the program. Seventy percent of eligible participants (n = 211) consented to participate and were randomized into the study. Forty seven of these participants did not complete the online baseline survey and therefore did not begin receiving text messages. The software program did not retain the randomization assignment of participants who did not begin to receive text messages. The randomization assignment of these 47 participants could not be recovered, precluding their inclusion in the ITT analyses. Thus, the final sample size (i.

e., the number of participants randomized and received at least one program message) was n = 164: 101 in the intervention and 63 in the control groups. Of the 1,331 ineligible participants, not seriously thinking about quitting in the next 30 days was the most Entinostat common reason (see Table A1). Figure 1. Stop My Smoking USA randomized controlled trial consort diagram. Four-week follow-up was conducted between April and June; and 3-month follow-up between June and August, 2011. Eighty-seven percent of participants responded at 4 weeks postquit and 80% at 3 months postquit.