A Cochrane review included 27 RCTs of family interventions to prevent smoking. There was moderate quality evidence family-based interventions had a positive impact on preventing smoking when compared to a no intervention control. The pooled estimate of studies reporting smoking uptake amongst baseline non-smokers detected a significant reduction in smoking behaviour in the intervention arms (risk ratio 0.76, 95% confidence interval 0.68 to 0.84; 9 trials, n=4810), but 8 studies with about 5000 participants could not be pooled because of insufficient data. Most of these studies used intensive interventions. Two studies in which some of the 4487 participants already had smoking experience at baseline did not detect evidence of effect (RR 1.04, 95% CI 0.93 to 1.17). 8 RCTs compared a combined family plus school intervention to a school intervention only. Of the 3 studies with data, 2 RCTS with outcomes for 2301 baseline never smokers detected evidence of an effect (RR 0.85, 95% CI 0.75 to 0.96) and one study with data for 1096 participants not restricted to never users at baseline also detected a benefit (RR 0.60, 95% CI 0.38 to 0.94). The other five studies with about 18,500 participants did not report data in a format allowing meta-analysis.
Comment: The quality of evidence is downgraded by study quality and by inconsistency (heterogeneity in interventions and outcomes).