Development of the Intervention Framework and Text Message Bank
PMT
The theoretical framework of the intervention was based on the transtheoretical model (TTM) and the protection motivation theory (PMT). Both models have been independently applied to health behavior change interventions.As determined using the app, smokers’ quitting intention to try to quit in the next 6 months was assessed on a 5-point scale, with 1 indicating not at all likely and 5 indicating very likely; a score of 1 to 3 points was considered a weak quitting intention, and 4 to 5 points was considered a strong quitting intentionOn the prequit date, messages related to consciousness raising, dramatic relief, and environmental reevaluation were provided to smokers with weak quitting intention. Messages related to stimulus control, self-liberation, and reinforcement management were provided to smokers with strong quitting intention. On the early quit and late quit dates, messages related to consciousness raising, dramatic relief, environmental reevaluation, and self-reevaluation were sent to smokers who had relapsed. Smokers who remained abstinent only received information based on the PMT.The text message bank was created using messages developed by the Peking University School of Public Health with the input of smokers and smoking cessation professionals. The messages had a 3-layer framework. The first layer was divided based on time and consisted of a prequit message, quit day message, withdrawal symptom management message, early quit message, and late period message. The second layer was divided based on the TTM, and the third layer was divided based on the PMT. The core motivational messages consisted of 14 subgroups with a total of 200 text messages; there were also approximately 200 contact messages. A more detailed description of the intervention framework based on the TTM and PMT and additional information about the text message bank are available in the eTable and eMethods in 