Twenty-four RCTs (37,339 participants, range 45 to 6,322) were included in the review. Quality assessment rated two trials as strong, 10 trials as moderate and 12 trials as weak. Seven RCTs used active recruitment methods and 16 RCTs used passive recruitment methods.
Overall proactive telephone counselling had a greater effect on point prevalence abstinence than self-help materials or no intervention control groups at six to nine months follow up (RR 1.26, 95% CI 1.11 to 1.43; 11 RCTs, Ι²=21.4%). There were no significant differences between intervention and control groups at 12 to 15 months after recruitment (13 RCTs, Ι²=0%). Results were similar for sub group analyses by recruitment channel and methodological quality.
Prolonged or continuous abstinence was greater at six to nine months for proactive telephone counselling (RR 1.58, 95% CI 1.26 to 1.98; seven RCTs, Ι²=49.1%) and at 12 to 18 months (RR 1.40, 95% CI 1.23 to 1.60; 13 RCTs, Ι²=18.5%) after recruitment compared to control. Results were similar regardless of recruitment method or quality at 12 to 18 months but at six to nine months results were not significant for active recruitment trials (one RCT) or for strong/moderate quality trials (three RCTs) compared to control groups.
Logistic regression found significant differences between active and passive groups at baseline in terms of smokers ready to quit and mean daily consumption across trials (details reported in review).