The longitudinal, bidirectional relationships between parent reports of child secondhand smoke exposure and child smoking trajectories.

This study examines the longitudinal relationships between child smoking and secondhand smoke exposure (SHSe). Participants were 222 parent-child dyads. The parents smoked, had a child with (48%) or without asthma, and were enrolled in a smoking/health intervention. Parent-reported child SHSe was measured at baseline and 4, 6, and 12-month follow-ups; self-reported child smoking was assessed at these points and at 2-months. A parallel process growth model was used. Baseline child SHSe and smoking were correlated (r = 0.30). Changes in child SHSe and child smoking moved in tandem as evidenced by a correlation between the linear slopes of child smoking and SHSe (r = 0.32), and a correlation between the linear slope of child smoking and the quadratic slope of child SHSe (r = - 0.44). Results may inform interventions with the potential to reduce child SHSe and smoking among children at increased risk due to their exposure to parental smoking.