Smoking status was assessed both as 7-day point prevalence abstinence (“Have you smoked at all, even a puff, in the last seven days?”) and continuous abstinence (smoking at all since the target quit day [TQD]) using a smoking calendar and the time-line follow-back method.23, 24 All of participants’ self-reports of smoking status during study visits were confirmed by an expired carbon monoxide (CO) level of less than 10 parts per million measured using a Micro-3 Smokerlyzer (Bedfont Scientific, USA, Williamsburg, VA).
