Competitions and incentives routinely feature in many smoking cessation programmes, in support of the quitting process. They are used either to encourage recruitment into the programme, or to reward cessation achieved at predefined stages.
There is a growing enthusiasm within the UK for incentive-based programmes to change unhealthy behaviours (NICE 2010). In 2007, the Tayside area of Scotland launched an incentive scheme for pregnant smokers, called 'Give It Up For Baby', in which grocery vouchers to the value of £12.50 per week were awarded for verified abstinence (Ballard 2009). While the interim report confirms that 140 women stopped smoking in the first year of the programme, the long-term validity of such initiatives for smoking cessation, especially once the rewards are withdrawn, remains to be determined.
A variety of rewards have been used for these purposes, including cash payments, salary bonuses, promotional items such as T-shirts, pens and bags, lottery tickets, raffles, holidays, and luxury goods such as cars or boats. Rewards can be given for attendance, irrespective of subsequent performance (i.e. guaranteed), or can be paid and scaled relative to the participant's success within the programme (i.e. contingent). Some workplace initiatives have operated a policy of disincentives, whereby employees have payments deducted for non-compliance with a smoking policy, but this is less frequently used than a system of positive rewards.
The workplace is a common setting for use of competitions and incentives. This is briefly addressed in a companion review from the Tobacco Addiction Group (Cahill 2008a), but we explore it more fully here. Most of the relevant studies have been conducted in the United States of America (USA), in part because of the structure of the healthcare system there, which obliges employers to cover health insurance costs for their workforce. In other countries, where the state or private insurance companies are the main healthcare provider, there may be less tangible incentive for employers to take direct responsibility for the health of their workers.
There are a number of advantages to offering smoking cessation support in the workplace, including the accessibility of the target population, the availability of occupational health support and the potential for peer pressure and peer support. Because of the existing salary and bonus structure, it is also relatively easy to set up a rewards system to supplement the programme, if that is the chosen mechanism. There are a number of smoking cessation studies in which groups are encouraged to compete against each other, either within a single workplace or between workplaces, often for material prizes as well as for financial incentives. More usually rewards are offered for individual participation or cessation, or both.
Quit and Win contests, and similar population-based initiatives, are examined in a companion review by the same authors (Cahill 2008b).
Some studies have tested incentives as a way of increasing participation in smoking cessation programmes. While this may be an effective method of boosting enrolment, any enhanced participation rate that incentives may deliver also must also be weighed against the stability of the long-term quit rates that are achieved. Incentives may also lead to increased rates of deception, either by participants falsely claiming to be abstinent, or by non-smokers taking part and then claiming to have quit. Individuals who elect to take part in a cessation programme that offers material rewards may be differently motivated from those who sign up to more conventional cessation methods, and this may be reflected in differential relapse rates.
The use of rewards and incentives increases the costs of running smoking cessation programmes. Tobacco control programmes need to assess whether the outlay is justified by the benefits that the component delivers. In other words, how many more quit attempters will join a programme that rewards their participation, and how much, if at all, is the quit rate enhanced by the end of programme follow up?
To assess the effects of competitions and incentives as aids to smoking cessation. We addressed the following questions:
1. Do competitions, contests and incentives reduce the prevalence of smoking and relapse?
2. Does the amount and type of incentive affect cessation and relapse prevention?
3. Do incentives improve recruitment to smoking cessation programmes, both within the community and within the workplace?
4. Does the amount and type of incentive affect recruitment?
5. What are the cost implications, to employers and to the community, of incentives and competitions?
6. Are incentives and competitions more or less effective in combination with other aids to recruitment, cessation and relapse prevention?
7. How great is the risk of disbenefits arising from the use of competitions and incentives, e.g. false claims, ineligible applicants?
Criteria for considering studies for this review
Types of studies
Randomized controlled trials allocating individuals, communities, workplaces or groups within workplaces to intervention or to control conditions.
Controlled trials with baseline measures and post-intervention outcomes
Types of participants
Adult smokers, of either gender, in any setting. We have not included trials aimed exclusively at adolescent smokers, as they are covered by other Cochrane reviews. We have not included trials aimed at pregnant smokers, since they are covered by the review Interventions for promoting smoking cessation during pregnancy (Lumley 2009).
Types of interventions
Contests, competitions, incentive schemes, lotteries, raffles, and contingent payments, to reward cessation and continuous abstinence in smoking cessation programmes. We have not included reports of the effectiveness of incentives or rewards to healthcare workers (physicians, nurses) for the delivery of smoking cessation interventions, as these will be covered in a forthcoming companion review. We have also excluded reimbursement to patients for smoking cessation treatment costs, as these are covered in another Cochrane review (Reda 2009).
Types of outcome measures
The primary outcome for this review is cessation rates, including point prevalence and sustained abstinence, for a minimum of six months from the start of the intervention, whether or not they are biochemically validated (Hughes 2003). The gold standard is biochemically verified sustained abstinence for at least six months. Trials which did not report cessation rates are excluded from this review.
Rates of recruitment to and participation in smoking cessation programmes, where they are reported in addition to cessation rates, but not where they are the primary outcome of interest.
Search methods for identification of studies
We searched the Cochrane Tobacco Addiction Group Specialized Register, which includes studies identified by systematic electronic searches of multiple databases, handsearching of specialist journals, and 'grey' literature (conference proceedings and unpublished reports not normally covered by most electronic indexing systems). In addition, we used specifically developed strategies to search four electronic databases, MEDLINE, EMBASE, CINAHL and PsycINFO. Search terms included incentive*, competition*, contest*, lotter*, reward*, prize*, contingent payment*, deposit contract*. The most recent searches were in November 2010.
Data collection and analysis
There were four stages in the review process:
Stage 1 One author prescreened all search results (abstracts), for possible inclusion or as useful background
Stage 2 Both authors independently assessed relevant studies for inclusion. We resolved discrepancies by consensus. We noted reasons for the non-inclusion of studies.
Stage 3 One author extracted data, and the second author checked them. This stage included an evaluation of quality. Both authors assessed each study according to the presence and quality of the randomization process, concealment of allocation, whether or not trialists and assessors were 'blinded', whether the analysis was appropriate to the study design, and the description of withdrawals and drop-outs.
Stage 4: Analysis:
The method of synthesizing the studies depended on the type, quality, design and heterogeneity of studies identified. We used the χ
We include the Tobacco Addiction Group's glossary of tobacco-related terms as an appendix (Appendix 1).
Description of studies
We identified 19 studies which met our inclusion criteria. All the included studies rewarded smoking cessation, either alone or in combination with recruitment or participation or both (See the Characteristics of included studies table for full details).
Seven of the studies were set in clinics or health centres (Crowley 1995 [COPD patients]; Gallagher 2007 [psychiatric patients, including people with schizophrenia]; Paxton 1980; Paxton 1981; Paxton 1983; Shoptaw (A) 2002 [narcotic abuse patients]; Volpp 2006), one in academic institutions (Tevyaw 2009), and the rest in worksites. Fourteen were based in the USA, three in the UK, one in Australia, and one in USA and Canada.
Two studies used lottery tickets as the incentive (Crowley 1995; Gomel 1993). Seven rewarded verified abstinence with cash payments (De Paul 1994; Gallagher 2007; Rand 1989; Shoptaw (A) 2002; Volpp 2006; Volpp 2009; Windsor (A) 1988). Three studies (Glasgow 1993; Hennrikus 2002; Koffman 1998) combined cash payments to individual quitters with one or more site-wide prize draws. Two trials rewarded individuals in the experimental group with cash payments based on their team's performance within the worksite (Klesges 1986; Klesges 1987).
Four studies (Maheu 1990; Paxton 1980; Paxton 1981; Paxton 1983) tested a system of deposits refunded for abstinence over the course of the programme. The Paxton studies compared possible reward schedules by varying the timing and the amount of deposits and repayments. Koffman 1998 required a non-refundable cash payment from the incentive programme registrants to entitle them to compete for staged cash rewards.
Four studies compared the effects of automatic payments with payments contingent upon cessation, with the guaranteed payment regimen generally serving as the control condition (Crowley 1995; Maheu 1990; Rand 1989; Tevyaw 2009).
Although all the studies rewarded smoking cessation as the primary outcome, several added incentives for other performance indicators. Participation and compliance were rewarded by Crowley 1995, Gallagher 2007, Glasgow 1993, De Paul 1994, Hennrikus 2002, Klesges 1986, Klesges 1987, Maheu 1990, Volpp 2006 and Volpp 2009. Koffman 1998 also paid those smokers who 'faded' their cigarettes to no more than 80 in the first month of the programme, as a preparation for stopping completely.
Only one trial (Glasgow 1993) of the 19 did not deploy any kind of cessation support programme.
Four of the earlier studies used aversive smoking as part of a multi-component programme (Maheu 1990; Paxton 1980; Paxton 1981; Paxton 1983). Five included nicotine replacement therapy to support their participants (Crowley 1995; Gallagher 2007; Maheu 1990 [supplementing aversive smoking]; Shoptaw (A) 2002; Volpp 2006).
The ten remaining studies all used some form of multi-component support programme. Five studies primarily offered a self-help programme (De Paul 1994; Gomel 1993; Koffman 1998; Rand 1989; Windsor (A) 1988), four offered individual or group counselling (Hennrikus 2002; Klesges 1986; Klesges 1987; Tevyaw 2009), while Volpp 2009 steered all participants towards locally-provided smoking cessation resources.
Risk of bias in included studies
Thirteen of the included studies were described as randomized (Crowley 1995; De Paul 1994; Gallagher 2007; Glasgow 1993; Gomel 1993; Hennrikus 2002; Klesges 1987; Rand 1989; Shoptaw (A) 2002; Tevyaw 2009; Volpp 2006; Volpp 2009; Windsor (A) 1988), with six of them also using stratification (Crowley 1995; De Paul 1994; Glasgow 1993; Hennrikus 2002; Volpp 2006; Volpp 2009). Two studies were described as 'quasi-experimental' (Klesges 1986; Koffman 1998). In the remaining four studies randomization was not used, with Maheu 1990 assigning two worksites to experimental or control status, and the Paxton trials allocating individual attenders to the next available treatment group.
Three studies (Volpp 2006; Volpp 2009; Windsor (A) 1988) were considered to have conducted adequate randomization procedures (sequence generation and allocation concealment), and a further two to have followed adequate procedures for sequence generation but possibly not for allocation concealment (Gallagher 2007; Shoptaw (A) 2002). Eight studies (De Paul 1994; Glasgow 1993; Gomel 1993; Hennrikus 2002; Klesges 1986; Klesges 1987; Rand 1989; Tevyaw 2009) were considered to have given insufficient detail for the integrity of the randomization to be assessed. The remaining studies either used inadequate randomization procedures or did not use randomization at all. Summary assessments of the risk of bias for key items in each study are shown in Figure 1. A sensitivity analysis excluding two studies (Gallagher 2007; Paxton 1980) which did not conceal allocation did not alter the overall findings (analysis not shown).
|Figure 1. Risk of bias summary: review authors' judgements about each risk of bias item for each included study.|
Because of the explicit mechanism of rewards, only four trials reported any attempt to blind participants, trialists or assessors (Crowley 1995; De Paul 1994; Tevyaw 2009; Volpp 2006). See the relevant risk of bias tables for details.
Drop-outs and losses to follow up
Eleven studies (Crowley 1995; De Paul 1994; Gallagher 2007; Glasgow 1993; Gomel 1993; Klesges 1987; Koffman 1998; Rand 1989; Volpp 2006; Volpp 2009; Windsor (A) 1988) treated programme drop-outs and losses to follow up as continuing smokers, and conducted the analyses on an intention-to-treat basis, i.e. the denominator included all persons randomized at the start of the trial in their original groups.
Raw outcome data, particularly in the older studies, were often difficult to extract, with 12 of the 19 studies presenting results as percentages only, in tabular or graphic form. Seven trials followed up participants for a maximum of six months (Crowley 1995; Klesges 1986; Klesges 1987; Paxton 1980; Paxton 1981; Rand 1989; Tevyaw 2009), two for between six and twelve months (Gallagher 2007; Volpp 2006), six for twelve months (Gomel 1993; Koffman 1998; Maheu 1990; Paxton 1983; Shoptaw (A) 2002; Windsor (A) 1988), one for 15 to 18 months (Volpp 2009), and three for 24 months (De Paul 1994; Glasgow 1993; Hennrikus 2002).
All the included studies used some form of biochemical validation procedure. Seventeen tested levels of cotinine (a metabolite of nicotine) in blood, saliva or urine, either at baseline to confirm initial smoking status (Crowley 1995; Gallagher 2007; Gomel 1993; Klesges 1986; Klesges 1987; Shoptaw (A) 2002; Windsor (A) 1988), to validate reports of abstinence (Crowley 1995; De Paul 1994; Gallagher 2007; Glasgow 1993; Gomel 1993; Klesges 1986; Klesges 1987; Maheu 1990; Tevyaw 2009; Volpp 2006; Volpp 2009; Windsor (A) 1988), among claimants of rewards (Hennrikus 2002) or among random samples of quitters (Hennrikus 2002; Paxton 1980; Paxton 1981; Paxton 1983). Eleven trials (Crowley 1995; De Paul 1994; Gallagher 2007; Glasgow 1993; Klesges 1986; Klesges 1987; Koffman 1998; Maheu 1990; Rand 1989; Shoptaw (A) 2002; Tevyaw 2009) verified abstinence by testing breath samples for carbon monoxide (CO) levels.
In order to test the robustness of the cessation interventions, we have included in our review only those studies which follow up participants for at least six months from the beginning of the intervention. Three of the trials, however, (Klesges 1986; Klesges 1987; Rand 1989) delivered their final cessation rewards six months into the programme, which was also the end of the designated follow-up period, thereby confounding the intervention rewards with testing at the longest follow up.
Appropriateness of analysis
Four of the eight trials which used a cluster-randomized design made due allowance for this in their analyses, either by testing for intra-class correlation (De Paul 1994; Glasgow 1993), by including worksite as a random effect (Hennrikus 2002) or by incorporating a nested design structure into the analyses of variance and testing retrospectively for intra-cluster correlations (though not in smoking prevalence) (Gomel 1993). The remaining four cluster-randomized trials did not report adjustments for the possible effects of clustering (Klesges 1986; Klesges 1987; Koffman 1998; Maheu 1990).
Crowley 1995 collapsed the three-way groupings for the six-month follow-up results, since differences between groups were by then negligible, and Windsor (A) 1988 collapsed the incentive/non-incentive groupings for analyses after the six-week assessment, as contradictory differences had emerged between the two pairs of groups. Our own analysis of Windsor (A) 1988 and Windsor (B) 1988 compares the effect of the smoking cessation components with and without the incentives.
Effects of interventions
Details of the results for the 19 included studies in this review are tabulated in the Analyses section (Analysis 1.1).
Only one trial (Volpp 2009) detected a significant effect of rewards, competitions or incentives on smoking abstinence at the longest follow up, and not confounded by rewards paid out for abstinence at that timepoint. At 15 or 18 months, quit rates for the incentivized and control groups were 9.4% vs 3.6% respectively (P = 0.001). A secondary endpoint in this trial was the completion of a smoking cessation programme, for which the intervention participants received a $100 payment. While all participants received information about local smoking cessation services, 15.4% of the intervention group enrolled in a cessation programme, compared with 5.4% of the controls (P < 0.001); 10.8% of the incentivized group completed the programme compared with 2.5% of the controls (P < 0.001).
We have conducted a descriptive meta-analysis of 11 of the included studies (13 comparisons), grouping by evaluation points (six to 24 months; Analysis 2.1). Because of high measures of heterogeneity between the studies (I
Two studies (De Paul 1994 and Windsor (A) 1988) had paid out their final reward to coincide with the six-month follow up, which may have compromised the results.
Analysis of cost benefits was not appropriate, since most of the trials failed to demonstrate a clinically significant long-term benefit of the intervention. However, cost considerations for Volpp 2009 are briefly discussed below.
Only one included study in this review offers evidence that incentives may improve long-term smoking cessation, whether conducted in the community, in healthcare settings or in the workplace. Volpp 2009 was a well-conducted trial, with adequate power and sufficiently robust long-term outcomes to raise the question of why its results are at variance with other trials in this review. The authors speculate that their study population was large enough (878 participants) to detect an effect, and that their rewards were substantial enough (a total of $750 available for completion of a smoking cessation programme and sustained abstinence at 9 or 12 months) to consolidate the target behaviour change. Six months after the final payment, the incentivized group maintained a higher quit rate than the control group. The trialists may have felt able to offer these considerable rewards because their trial design did not require them to provide and fund their own smoking cessation programme; instead, they encouraged their participants to avail themselves of local smoking cessation services, thereby freeing up resources to enhance the reward schedule. While the findings of this trial are promising, such a paradigm may only work in communities or situations where independent and well-resourced smoking cessation services already operate.
Many of the early studies were underpowered and of variable quality. Three studies (Klesges 1986; Klesges 1987; Rand 1989) confounded the final delivery of cessation rewards with the final follow-up assessment. Similarly, although De Paul 1994 and Koffman 1998 reported significantly higher cessation rates for the incentives groups at the six-month assessment, this evaluation coincided with the final phase of the rewards programmes. At later follow up points in these studies all such differences had disappeared. The only early study (Maheu 1990) to detect a clear difference between the long-term quit rates of the intervention and control groups (50% versus 25%) was not randomized, had too small a sample to reach statistical significance, tested the allocation of incentives rather than the presence or absence of them, and may have confounded the intervention programme by including a sponsorship component which was not offered in the control site. Encouraging early quit rates at 30 days (Volpp 2006) and at 21 days (Tevyaw 2009) dwindled to non-significant differences by the six-month follow ups. Although Gallagher 2007 achieved significantly different CO-validated quit rates, the cotinine-validated quit rates did not achieve clinically significant differences, suggesting that while some participants could achieve temporary abstinence for their clinic visit, the more rigorous urinary cotinine test did not indicate abstinence sustained beyond a few hours.
Glasgow 1993 reported one-year cessation rates for HIP participants more than double those of non-registrants (22.1% versus 9.4%, P < 0.005), but this difference had become non-significant at the two-year follow up; and again, the one-year evaluation was very close to the final lottery draw for HIP participants and may well have been influenced by that proximity. Gomel 1993 indicated that at three months (two weeks after programme end) the incentives group had a quit rate of 20%, compared with 17% in the comparison (BC) group, but that by 12 months the rates had switched to 20% for the BC group compared with 4% for the incentives group (estimated from graphical percentage figure). Shoptaw (A) 2002 reported the same long-term pattern of relapse, with significant benefit to the contingency management groups in the first three months rapidly vanishing over the nine-month post-programme follow-up period.
The picture that emerges from these examples is that incentives may improve compliance while they are in place, but that once they are withdrawn the normal pattern of relapse is likely to re-establish itself. Although many of the studies in this review were underpowered to detect sustained effects, we have explored the likelihood of erosion of the intervention effect at longest follow up (Figure 2). We include only those studies which followed up participants beyond the six-month assessment point (the 12-month assessment point, in the case of Glasgow 1993). This scatterplot suggests that for studies with positive effects (OR greater than 1 at six months), there is evidence for an erosion of intervention effect over time (De Paul 1994; Windsor (A) 1988; Shoptaw (B) 2002; Volpp 2009). For studies with negative effects (OR less than 1 at six months, or 12 months for the Glasgow trial) the relationship is less clear, with two trials (Windsor (B) 1988; Gomel 1993) showing an erosion of effect, and two (Glasgow 1993; Shoptaw (A) 2002) demonstrating an increased effect over time. Neither increase, however, achieved statistical significance.
|Figure 2. Erosion of intervention effect over time, based on ORs at longest follow up. The X axis represents the OR at 6m assessment (12m for Glasgow 1983), and the Y axis the OR at longest follow up (12, 18 or 24m).|
The use of tangible rewards will always be a trade-off between maximizing participation and attracting smokers who are motivated more by the rewards than by the wish to stop smoking. The type and scale of the incentive has therefore been considered a critical element in the design of a cessation programme, although from the perspective of this review, which is primarily concerned with sustained or permanent cessation, the type and scale of the incentives may be less significant than the negative effects of removing them altogether. The incentives varied considerably across the studies in this review, including cash prizes, vouchers for goods and services, state lottery tickets, prize draws, a catered meal and combinations of cash and state lottery tickets. Only the Volpp 2009 trial, with substantial cash payments both for compliance and for prolonged abstinence, demonstrated a sustained beneficial effect beyond the expiry of the payment schedule. However, participants in this trial were all employees of a large American company, were predominantly white, and enjoyed relatively high levels of education and income. The success of this trial may not be readily generalisable to other populations of smokers, with different regional, socio-economic and ethnic mixes.
In this review we have included only those studies which specified smoking cessation as a primary outcome, and which applied the intervention rewards to achievement of abstinence. However, higher recruitment rates may have a role to play in improving long-term cessation rates. A recurrent feature of several studies in this review, both included and excluded, was the effect of incentives upon participation rates. A widespread assumption seemed to be that, since incentives are frequently shown to improve participation rates in cessation programmes, this would surely lead to higher quit rates (Grunberg 1990; USDHHS 1989). Our review has not found this to be the case. While the studies' authors noted the effectiveness of immediate or possible rewards in raising recruitment levels, this was generally not reflected in the long-term cessation rates (Hennrikus 2002; Klesges 1986; Maheu 1990; Paxton 1983; Volpp 2006). The primary outcome of the Volpp 2006 study, for example, was to enhance enrolment into a free cessation programme by offering incentives for attendance, compliance and cessation. Although the incentives doubled participation rates (41.3% of invitees versus 19.5%), the confirmed six-month cessation rates were low in both groups (6.5% versus 4.6%), with negligible difference between the absolute numbers of quitters.
Given the potential for incentives to improve recruitment rates, the absolute numbers of successful long-term quitters may in some cases be increased, even if cessation rates do not differ between the intervention and control groups. It is plausible that incentives may have value as a mechanism for cessation induction, as distinct from their role in aiding or enhancing the cessation process (Hughes 2003).
All the included studies in this review used some form of biochemical verification to confirm the smoking status of those claiming abstinence. While this procedure is now the recommended gold standard for good trial design (Benowitz 2002), it is particularly important that quitters in an incentives- or competition-based trial are shown to be truly abstinent at the evaluation points. Eligibility for cessation rewards depended in all the included studies upon biochemical confirmation of the claim of abstinence.
Three of the studies in this review reported a good correspondence between claims of abstinence and their biochemical verification, with Koffman 1998 noting a 96% agreement, Windsor (A) 1988 100% agreement for more than 600 saliva thiocyanate samples, and De Paul 1994 a 95% agreement. Maheu 1990 used the 'bogus pipeline' method (i.e. collecting saliva samples but not testing them for cotinine), but also verified abstinence throughout by CO testing. The Paxton studies took random urine samples to deter false reporting, and also occasionally cross-checked smoking status with family members or friends. They reported that levels of deception were 'very low', and attributed this to having warned subjects in advance about the random biochemical checks.
Three studies which targeted high-risk smoking groups went to some trouble to control for possible levels of deception. Crowley 1995, dealing with moderately-ill COPD patients who had been co-opted into the programme, anticipated a measure of deception, and calculated an expected ratio of CO divided by cigarettes smoked. This confirmed a greater disparity between cigarettes smoked and numbers reported among the non-verified self-report group and the control group than among the intervention group, who were rewarded only for verified abstinence. Shoptaw (A) 2002, dealing with methadone-maintained drug abusers with high levels of smoking, reported similar findings between self-reported abstinence and its biochemical verification, but cautioned that it was possible that participants had found ways of subverting the breath-testing schedule. Against this possibility, however, was the fact that subjects had averaged only 44% of the available prize vouchers for abstinence, suggesting that any subversion had not been particularly successful. Gallagher 2007, dealing with smokers with schizophrenia or other serious mental disorders, found considerable disparities between quit claims validated by CO breath samples (confirming abstinence for a few hours) and those validated by urinary cotinine (a few days of abstinence). This need not indicate deception, but suggests that the achieved abstinence for which the rewards were being claimed was not robust or sustained (SRNT 2002).
The two studies which found a striking disparity between self-reported abstinence and biochemical verification of the claims were both large, worksite-based, cluster-randomized trials, which followed their subjects for 24 months. Hennrikus 2002 reported a 33.6% mismatch between self report and confirmation at 24 months, and Glasgow 1993 a 27% mismatch at the12-month evaluation. Both trials had 'sprung' the biochemical validation requirement on the quitters at follow up. The clear discrepancies suggest that people responding indirectly (not face-to-face) to a question about their smoking, and not expecting to have their answer checked, may be significantly more likely to say what they think the questioner wants to hear.
Implications for practice
Implications for research
We would like to thank Suzanne Colby, Sandra Gallagher, Leonard Jason, Susan McMahon, Erin Rotherham-Fuller, Damaris Rohsenow, Steven Shoptaw, Tracy Tevyaw and Kevin Volpp for supplying additional data or clarification, and Harry Lando and Esteve Salto for commenting on an earlier version of this review.
Data and analyses
- Top of page
- Authors' conclusions
- Data and analyses
- What's new
- Contributions of authors
- Declarations of interest
- Sources of support
- Index terms
Appendix 1. Glossary of tobacco-related terms
Last assessed as up-to-date: 23 November 2010.
Protocol first published: Issue 2, 2003
Review first published: Issue 2, 2005
Contributions of authors
KC and RP extracted data. KC wrote the review, with comments from RP. RP conducted the statistical analysis and the forest plots.
Declarations of interest
Sources of support
- Department of Primary Health Care, Oxford University, UK.
- National School for Health Research School for Primary Care Research, UK.
- NHS Research and Development Fund, UK.
Medical Subject Headings (MeSH)
MeSH check words
* Indicates the major publication for the study