Abstract
BACKGROUND
Financial incentives (money, vouchers, or self-deposits) can be used to positively reinforce smoking cessation. They may be used as one-off rewards, or in various schedules to reward steps towards sustained smoking abstinence (known as contingency management). They have been used in workplaces, clinics, hospitals, and community settings, and to target particular populations. This is a review update. The previous version was published in 2019.
OBJECTIVES
Primary To assess the long-term effects of incentives and contingency management programmes for smoking cessation in mixed and pregnant populations. Secondary To assess the long-term effects of incentives and contingency management programmes for smoking cessation in mixed populations, considering whether incentives were offered at the final follow-up point. To assess the difference in outcomes for pregnant populations, considering whether rewards were contingent on abstinence or guaranteed.
SEARCH METHODS
For this update, we searched CENTRAL, MEDLINE, Embase, PsycINFO, and two trials registers on 2 November 2023, and the Cochrane Tobacco Addiction Group Specialised Register on March 2023, together with reference checking, citation searching, and contact with study authors to identify additional studies.
SELECTION CRITERIA
We considered only randomised controlled trials (RCTs), allocating individuals, workplaces, groups within workplaces, or communities to smoking cessation incentive schemes or control conditions. We included studies in a mixed-population setting (e.g. community-, work-, clinic- or institution-based), studies with specific populations (e.g. those with diagnosed mental health conditions), and studies in pregnant people who smoke.
DATA COLLECTION AND ANALYSIS
We used standard Cochrane methods. The primary outcome measure in the mixed-population studies was abstinence from smoking at longest follow-up (at least six months from the start of the intervention). In the trials of pregnant people, we used abstinence from smoking measured at the longest follow-up, and at least to the end of the pregnancy. Where available, we pooled outcome data using a Mantel-Haenszel random-effects model, with results reported as risk ratios (RRs) and 95% confidence intervals (CIs), using adjusted estimates for cluster-randomised trials. We analysed studies carried out in mixed populations separately from those carried out in pregnant populations.
MAIN RESULTS
Forty-eight mixed-population studies met our inclusion criteria, recruiting more than 21,924 participants; 15 of these are new to this version of the review. Studies were set in varying locations, including community settings, clinics or health centres, workplaces, and outpatient drug clinics. We judged eight studies to be at low risk of bias, and 16 to be at high risk of bias, with the remaining 24 studies at unclear risk. Thirty-three of the trials were run in the USA, two in Thailand, one in the Philippines, one in Hong Kong, and one in South Africa. The rest were European. Incentives offered included cash payments, self-deposits, or vouchers for goods and groceries, offered directly or collected and redeemable online. The pooled RR for quitting with incentives at longest follow-up (six months or more) compared with controls was 1.52 (95% CI 1.33 to 1.74; I2 = 23%; 39 studies, 18,303 participants; high-certainty evidence). Results were not sensitive to the exclusion of seven studies that offered an incentive for cessation at long-term follow-up (result excluding those studies: RR 1.46, 95% CI 1.23 to 1.73; I2 = 26%; 32 studies, 15,082 participants), suggesting the impact of incentives continues for at least some time after incentives cease (at least six months). For this update, we included an adjusted analysis incorporating three cluster-RCTs. The pooled odds ratio was 1.57 (95% CI 1.37 to 1.79; I2 = 30%; 43 studies, 23,960 participants; high-certainty evidence). Although not always clearly reported, the total financial amount of incentives varied considerably between trials, from zero (self-deposits), to a range of between 45 US dollars (USD) and USD 1185. There was no clear difference in effect between trials offering low or high total value of incentives, nor those encouraging redeemable self-deposits. We ran an updated exploratory meta-regression and found no significant association between the outcome and the total value of the financial incentive (P = 0.963). Any such indirect comparison is particularly crude in this context, due to differences in the cultural significance of financial amounts (e.g. USD 50 might have different significance in different contexts). We included 14 studies of 4314 pregnant people (11 conducted in the USA, one in France, and two in the UK). We judged four studies to be at low risk of bias, two at high risk of bias, and eight at unclear risk. When pooled, the 13 trials with usable data delivered a risk ratio at longest follow-up (up to 48 weeks postpartum) of 2.13 (95% CI 1.58 to 2.86; I2 = 31%; 13 studies, 3942 participants; high-certainty evidence), in favour of incentives.
AUTHORS' CONCLUSIONS
Overall, our conclusion from this latest review update remains that there is high-certainty evidence that incentives improve smoking cessation rates at long-term follow-up in mixed population studies. The evidence demonstrates that the effectiveness of incentives is sustained even when the last follow-up occurs after the withdrawal of incentives. There is also now high-certainty evidence that incentive schemes conducted amongst pregnant people who smoke improve smoking cessation rates, both at the end of pregnancy and postpartum. This represents a change from the previous update in which we rated this evidence as moderate certainty. Current and future research might more precisely explore differences between trials offering low or high cash incentives and self-incentives (deposits), within a variety of smoking populations, focusing on low- and middle-income countries where the burden of tobacco use remains high.
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