Discussion
RECRUITMENT
This was the first randomized controlled trial of a JITAI smartphone app for smoking cessation that uses passive measurement to trigger behavioral support. The automated online trial design employed was feasible and successful in reaching the target sample size within the relatively short recruitment timeframe. The cost per participant was compared favorably with other online digital cessation trials.The trial also demonstrated that three-quarters of smokers assigned to the Quit Sense app would install it on their phones and engage with it at least to the point of setting a quit date. Very few evaluations report the uptake rates for cessation apps and those that do have either offered incentives for installationTrial findings provided promising evidence that Quit Sense increased verified cessation at 6 months compared to usual care, though with considerable imprecision in line with a feasibility trial and due to low return rates of saliva samples. No between-arm differences were observed at 6 weeks of follow-up, suggesting any benefit from Quit Sense, relative to usual care, was more likely because of maintaining abstinence in the longer term rather than from increasing the proportion of participants initiating a quit attempt. However, there was no quantitative evidence that Quit Sense affected the hypothesized mechanisms of action at 6 weeks of follow-up. The qualitative process evaluation provided some insights into how Quit Sense was felt to bring about abstinence among those participants interviewed and is reported elsewhere.