A dyadic planning intervention to quit smoking in single-smoking couples: design of a randomized controlled trial.

BACKGROUND: Tobacco use is the largest preventable cause of death. Smoking cessation interventions that use implementation intentions show promising results. Implementation intentions are if-then plans that specify a certain behaviour within a situational context. This study will examine whether involving a non-smoking partner could improve planning interventions, and whether and which partner interactions underlie this effectiveness.

METHODS: This single-blind randomized controlled trial has a longitudinal design with a baseline questionnaire, end-of-day measurements for three weeks starting on the quit date, and a follow-up questionnaire after three months.

PARTICIPANTS: single-smoking couples who live together and are in a relationship for more than one year.

SETTING: couples are randomized to either a dyadic or individual planning condition. After the intervention the smoker attempts to quit smoking and the diary measurements start.

MEASUREMENTS: The primary outcome variable is smoking abstinence. Secondary outcome measures are smoking behaviour and relationship satisfaction. Partner interactions are examined as a possible mediator.

DISCUSSION: This RCT is the first to examine the effectiveness of dyadic planning to quit smoking in single-smoking couples. Partner interactions are thought to play an important role during the quit attempt, and therefore in the effectiveness of the intervention. This RCT will provide more insight into which daily partner interactions are beneficial for smoking abstinence and the couples' relationship satisfaction, and whether the type of intervention is related to different types or levels of partner interactions and smoking behaviour. When proven effective, this planning intervention in combination with coaching for the non-smoking partner will be a valuable and low-cost addition to existing smoking interventions.

TRIAL REGISTRATION: The trial is retrospectively registered on 19/04/2017 on www.trialregister.nl ( TC: 6398 ).