Estimating the true effectiveness of smoking cessation interventions under variable comparator conditions: a systematic review and meta-regression.

Comparator variability and underreporting of comparators obscures the interpretation, comparison and generalisability of behavioural smoking cessation trials. Comparator variability should thus be taken into account when interpreting and synthesising evidence from trials. Otherwise, policy makers, practitioners and researchers may draw incorrect conclusions about the (cost)effectiveness of smoking cessation interventions and their constituent components.