Differences in the effectiveness of individual-level smoking cessation interventions by socioeconomic status

People from lower socioeconomic groups are more likely to smoke and less likely to succeed in achieving abstinence, making tobacco smoking a leading driver of health inequalities. Contextual factors affecting subpopulations may moderate the efficacy of individual-level smoking cessation interventions. It is not known whether any intervention performs differently across socioeconomically-diverse populations and contexts. To assess whether the effects of individual-level smoking cessation interventions on combustible tobacco cigarette use differ by socioeconomic groups, and their potential impact on health equalities. We searched the Cochrane Database of Systematic Reviews from inception to 1 May 2023 for Cochrane reviews investigating individual-level smoking cessation interventions. We selected studies included in these reviews that met our criteria. We contacted study authors to identify further eligible studies. We included parallel, cluster or factorial randomised controlled trials (RCTs) investigating any individual-level smoking cessation intervention which encouraged complete cessation of combustible tobacco cigarette use compared to no intervention, placebo, or another intervention in adults. Studies must have assessed or reported smoking quit rates, split by any measure of socioeconomic status (SES) at longest follow-up (≥ six months), and been published in 2000 or later. We followed standard Cochrane methods for screening, data extraction, and risk of bias assessment. We assessed the availability of smoking abstinence data by SES in lieu of selective reporting. The primary outcome was smoking cessation quit rates, split by lower and higher SES, at the longest follow-up (≥ six months). Where possible, we calculated ratios of odds ratios (ROR) with 95% confidence intervals (CIs) for each study, comparing lower to higher SES. We pooled RORs by intervention type in random-effects meta-analyses, using the generic inverse-variance method. We subgrouped by type of SES indicator and economic classification of the study country. We summarised all evidence in effect direction plots and categorised the intervention impact on health equality as: positive (evidence that the relative effect of the intervention on quit rates was greater in lower rather than higher SES groups), possibly positive, neutral, possibly neutral, possibly negative, negative, no reported statistically significant difference, or unclear. We evaluated certainty using GRADE. We included 77