BMJ Open: first published as 10.1136/bmjopen-2016-011045 on 9 June 2016. Downloaded from
`
`http://bmjopen.bmj.com/
`
` on February 27, 2024 by guest. Protected by copyright.
`
`Open Access
`
`Research
`
`Estimating the number of quit attempts
`it takes to quit smoking successfully in
`a longitudinal cohort of smokers
`
`Michael Chaiton,1,2 Lori Diemert,1 Joanna E Cohen,1,2,3 Susan J Bondy,1,2
`Peter Selby,1,2 Anne Philipneri,1 Robert Schwartz1,2
`
`To cite: Chaiton M,
`Diemert L, Cohen JE, et al.
`Estimating the number of quit
`attempts it takes to quit
`smoking successfully in a
`longitudinal cohort of
`smokers. BMJ Open 2016;6:
`e011045. doi:10.1136/
`bmjopen-2016-011045
`
`▸ Prepublication history for
`this paper is available online.
`To view these files please
`visit the journal online
`(http://dx.doi.org/10.1136/
`bmjopen-2016-011045).
`
`Received 5 January 2016
`Revised 11 April 2016
`Accepted 18 May 2016
`
`ABSTRACT
`Objectives: The number of quit attempts it takes a
`smoker to quit successfully is a commonly reported
`figure among smoking cessation programmes, but
`previous estimates have been based on lifetime recall
`in cross-sectional samples of successful quitters only.
`The purpose of this study is to improve the estimate of
`number of quit attempts prior to quitting successfully.
`Design: We used data from 1277 participants who
`had made an attempt to quit smoking in the Ontario
`Tobacco Survey, a longitudinal survey of smokers
`followed every 6 months for up to 3 years beginning in
`2005. We calculated the number of quit attempts prior
`to quitting successfully under four different sets of
`assumptions. Our expected best set of assumptions
`incorporated a life table approach accounting for the
`declining success rates for subsequent observed quit
`attempts in the cohort.
`Results: The estimated average number of quit
`attempts expected before quitting successfully ranged
`from 6.1 under the assumptions consistent with prior
`research, 19.6 using a constant rate approach, 29.6
`using the method with the expected lowest bias, to
`142 using an approach including previous recall
`history.
`Conclusions: Previous estimates of number of quit
`attempts required to quit may be underestimating the
`average number of attempts as these estimates
`excluded smokers who have greater difficulty quitting
`and relied on lifetime recall of number of attempts.
`Understanding that for many smokers it may take 30
`or more quit attempts before being successful may
`assist with clinical expectations.
`
`1Ontario Tobacco Research
`Unit, Toronto, Ontario,
`Canada
`2Dalla Lana School of Public
`Health, University of Toronto,
`Toronto, Ontario, Canada
`3Johns Hopkins Bloomberg
`School of Public Health,
`Baltimore, Maryland, USA
`
`Correspondence to
`Dr Michael Chaiton;
`Michael.chaiton@utoronto.ca
`
`INTRODUCTION
`Tobacco use is the number one cause of pre-
`ventable mortality. Five million deaths each
`year are attributable to smoking, with an esti-
`mated rise to as much as 10 million deaths
`per year by the 2030s.1 Yet, despite the wide-
`spread awareness of the harms of smoking,
`millions continue to smoke around the world
`partly due to the difficulty it takes to quit
`smoking.
`
`Strengths and limitations of this study
`
`▪ Uses multiple methodologies to improve upon
`estimates of the number of attempts it takes a
`smoker to quit.
`▪ Novel use of life table methodology to overcome
`issues of censoring.
`▪ Population estimates of cessation derived from a
`large,
`longitudinal, population representative
`study designed to assess smoking cessation
`every 6 months for up to 3 years.
`▪ Findings reflect a population average and are not
`individually predictive.
`▪ The definition used of a successful quit was ces-
`sation to 1 year, but significant
`likelihood of
`relapse for some after that point.
`
`reported to have said,
`Mark Twain is
`‘Quitting smoking is easy: I’ve done it thou-
`sands of times’. Smoking cessation is a diffi-
`cult and complex process, and smokers use
`many methods and approaches to achieve
`cessation. Knowing how many quit attempts
`it takes an average smoker to quit is import-
`ant as it can frame different narratives about
`the quitting process. This information can be
`used to inform smoking cessation advice and
`important messages to stay engaged in the
`process of quitting. Alternatively, knowing
`the average number of quit attempts may be
`a deterrent to continue trying.
`For
`this
`reason,
`the number of quit
`attempts it takes before smokers are success-
`ful at quitting is a statistic that figures promi-
`nently in much of the literature on smoking
`cessation programmes. For
`instance,
`the
`American Cancer Society suggests
`that
`it
`attempts,2 while
`8–10
`takes
`quit
`the
`Australian Cancer Council suggests that it is
`12–14 attempts.3 The Centers for Disease
`8–11
`Control
`and
`Prevention suggests
`attempts before quitting permanently.4 Many
`practitioners believe that it takes five to seven
`attempts.5 One document on smoking cessa-
`tion by a maker of
`smoking cessation
`
`Chaiton M, et al. BMJ Open 2016;6:e011045. doi:10.1136/bmjopen-2016-011045
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`attempts, whereas those who struggle may repeatedly try
`and relapse, making the average success rate for early
`quit attempts higher than subsequent ones. Partos and
`colleagues found that smokers who had one or more
`recent failed quit attempts were indeed less likely to quit
`successfully.16
`It may be possible to improve on the estimate of the
`number of quit attempts prior to quitting successfully.
`A standard life table translates cross-sectional age-
`specific mortality rates into a theoretical cohort lasting
`from birth to death.17 The same probability approach
`could be used to model the change in a hypothetical
`cohort of quitting smokers where the probability of exit
`changes by ‘quit age’ (1 for first attempt, 2 for second
`attempt, and so on). This approach would translate
`cross-sectional (longitudinally observed but in a cross-
`section of time) quit attempt-specific success rates into
`a theoretical cohort lasting from the first to the last
`quit attempt. The calculation of the chance of success
`based on the number of previous quit attempts would
`allow for a calculation of an average of the number of
`attempts to quit that does not depend on an assump-
`tion that quit attempts are independent events. This
`approach would also allow for the inclusion of unsuc-
`cessful quitters into the average that were not included
`in previous work.
`The purpose of this paper is to improve on the litera-
`ture estimating the number of attempts it takes to quit
`smoking successfully by calculating the number under
`four different sets of assumptions.
`
`METHODS
`Participants
`We primarily used data from the Ontario Tobacco
`Survey (OTS), a population-based longitudinal panel
`survey of smokers (18 years of age and over) in Ontario,
`Canada. Smokers were followed for up to 3 years at
`∼6-month intervals (baseline survey plus 6 follow-ups)
`with recruitment beginning in 2005. Recruitment was
`staggered so that the survey interviews were conducted
`between 2005 and 2011. The smoker response rate was
`61%. Participants were selected through random digit
`dialling stratified by region of Ontario, and character-
`istics of the sample were consistent with census data
`from Ontario.18 Further details of the questionnaire,
`variables, sampling and recruitment processes are docu-
`mented online at http://otru.org/research-evaluation/
`ontario-tobacco-survey/ots-technical-documentation/.18
`The full sample consisted of 4501 recent (past 6-month
`smokers) of those 4501 recent smokers and 3960 were
`current (past month smokers). For this study, to study
`quit
`attempt-specific quit
`rates, only
`respondents
`(n=1277) identified as current smokers (past month) at
`baseline and who self-reported a serious quit attempt at
`follow-up 1, follow-up 2 or follow-up 3 were included.
`The eligible participants made a total of 3362 quit
`attempts. Previous studies of the OTS have examined
`
`Open Access
`
`medication6 cites that most smokers quit five to seven
`times before they succeed, referencing a review article,7
`which refers to a 1995 Epidemiological Review article8
`that only indirectly refers to this statistic.
`We know that the likelihood of quitting smoking on
`any given quit attempt is low;9 however, providing an
`accurate determination of the number of quit attempts
`the average smoker takes to succeed is extremely diffi-
`cult. Current estimates appear to come from recalled
`lifetime quit attempts among smokers who had success-
`fully quit. For
`instance, a recent Gallup poll of
`Americans found that former smokers had made an
`average of 6.1 quit attempts before quitting success-
`fully.10 The cross-sectional Canadian Tobacco Use
`Monitoring Survey reported that former smokers had
`3.2 prior quit attempts.11 Similarly, the estimate of 12–14
`attempts reported by Zhu et al12 was derived from cross-
`sectional data in California. However, the use of cross-
`sectional data has severe limitations, as it depends on a
`smoker’s ability to remember past quit attempts over a
`lifetime. The number of recalled quit attempts is signifi-
`cantly lower in cross-sectional assessments compared
`with longitudinal assessments.13 These estimates are also
`biased as
`they only account
`for successful quitting
`among people who are able to quit and do not consider
`all quit attempts from those whose data were censored—
`those who have yet to succeed. Consequently, we should
`expect that the real number of attempts prior to quitting
`successfully should be substantially higher than these
`estimates.
`One study suggests that these estimates are too low.
`Borland et al used data from the longitudinal Inter-
`national Tobacco Cohort to estimate that the average
`smoker had made 40 attempts by the age of 40.13 While
`Borland’s study does not directly address the question of
`average number of quit attempts taken before quitting
`successfully, it demonstrates that smokers attempt to quit
`at the rate of approximately once per year. If it did take
`five to seven attempts to quit successfully, at an average of
`one quit attempt per year, we would expect to see very
`few smokers over the age of 30 years.
`If we assume that each quit attempt is an independent
`event, this allows us to use basic probability to come up
`with the geometric mean, which is calculated by dividing
`1 by the probability of that event. If it does take five to
`seven attempts on average as suggested, then one must
`assume that the success rate for each attempt is some-
`where between 14% and 20%—a figure that does not
`consistently align with the literature for
`long-term
`success.4 9 14 15 Thus, we should expect, a priori, that
`the lifetime number of quit attempts should be substan-
`tially higher than the five to seven attempts figure.
`However,
`the real number of attempts needed to
`succeed should be even higher, as the assumption of
`independence of quit attempts
`is not realistic. We
`should expect that the average chance of success will
`decrease over repeated quit attempts. Those who will
`have an easier time quitting will
`succeed on early
`
`2
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`Chaiton M, et al. BMJ Open 2016;6:e011045. doi:10.1136/bmjopen-2016-011045
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`
` on February 27, 2024 by guest. Protected by copyright.
`
`Open Access
`
`more likely to be male than were those who were
`included in the analysis; however, there was no differ-
`ence in smoking behaviours (self-perceived addiction,
`intentions to quit, daily smoking status and number of
`cigarettes smoked per day) for those with follow-up data
`compared with those without follow-up data. Of those
`participants who made an eligible quit attempt, 91 were
`lost to follow-up before a successful or unsuccessful quit
`attempt could be ascertained (see table 2). Adjusting for
`time in study, there were no differences in demographics
`or smoking behaviours comparing with lost to follow-up
`to other eligible participants.
`
`Measures
`Lifetime quit attempts at baseline: At baseline, participants
`were asked, ‘How many times have you EVER made a
`serious attempt to quit smoking? By serious, we mean
`that you made a conscious attempt to stay off cigarettes
`for good’.
`Quit attempts over follow-up: At each follow-up, respon-
`‘In the past 6 months, how many
`dents were asked,
`times did you make a serious attempt to quit smoking?
`By serious, we mean that you made a conscious attempt
`to stay off cigarettes for good’.
`Successful quit: A successful quit was defined as one
`that lasted for at least 1 year, as assessed by self-reported
`time since last cigarette. Time since last cigarette was
`asked at each follow-up by asking participants, ‘Have you
`smoked a cigarette since we last spoke with you in [Date
`of Interview]?’ and ‘How long ago was it that you last
`smoked a cigarette?’ All available follow-up data were
`used to assess successful quitting until at least 1 year
`without relapse had occurred.
`
`Statistical analysis
`This study takes four different approaches to estimating
`the number of quit attempts each with their own sets of
`limitations. These analyses are descriptive of the data.
`The first method is a count of the number of attempts;
`the second is the calculation of the mean based on a
`simple probability calculation; Methods 3 and 4 rely on
`a novel use of a life table analysis. Probability of quitting
`successful for each of the methods, both overall and quit
`
`Table 2 Number of eligible participants lost to follow-up
`prior to ascertainment of outcome
`
`Number lost prior to
`outcome ascertainment
`Follow-up number
`0*
`1
`1
`2
`12
`3
`30
`4
`7
`5
`41
`6
`*Participants were required to complete at least one follow-up to
`be eligible for inclusion.
`
`the predictors associated with making a quit attempt
`and the individual risk factors associated with successful
`quitting in this cohort, which include fewer previous
`quit attempts, higher level of education, belief that it
`would not be hard to quit and lower perceived addi-
`ction.18 The characteristics of the sample are representa-
`tive of
`the characteristics of smokers making a quit
`attempt in Ontario (see table 1). The OTS was approved
`by the institutional review boards of the University of
`Toronto and the University of Waterloo.
`Among eligible participants at baseline, only 400
`(10.1%) did not provide follow-up data. Those without
`follow-up data were younger (37.6 vs 44.2 years) and
`
`Table 1 Characteristics of current smokers at baseline in
`the Ontario Tobacco Survey who had made at least one
`quit attempt (n=1277)
`Characteristic
`
`Per cent
`
`n
`
`Sex
`Female
`Male
`Age
`18–24
`25–34
`35–44
`45–54
`55–64
`65+
`Marital status
`Married
`Single
`Education
`Less than high school
`High school or more
`Children at home
`No
`Yes
`Ever used pharmacotherapy
`No
`Yes
`Ever used behavioural therapy
`846
`No
`431
`Yes
`Number of previous quit attempts at baseline
`0
`97
`1
`250
`2
`244
`3
`211
`4
`123
`5 or more
`352
`Frequency of smoking at baseline
`Daily smoker (every day)
`Occasional smoker (less than daily)
`Heaviness of smoking index
`57.0
`728
`Low
`43.0
`549
`Medium/high
`Heaviness of smoking index calculated from daily cigarette
`consumption and the time to first cigarette after waking (scores of
`0–2 were classified as low, 3–6 as high).19
`
`57.3
`42.7
`
`10.7
`17.1
`22.8
`26.6
`14.5
`8.3
`
`56.5
`43.5
`
`15.0
`85.0
`
`58.4
`41.6
`
`41.5
`58.5
`
`66.2
`33.8
`
`7.6
`19.6
`19.1
`16.5
`9.6
`27.6
`
`85.5
`14.5
`
`732
`545
`
`137
`218
`291
`340
`185
`106
`
`721
`556
`
`192
`1085
`
`746
`531
`
`530
`747
`
`1092
`185
`
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`
`Open Access
`
`attempt number specific, is based on observational data
`from the OTS. We calculated the estimate for each
`method across the overall sample, as well as within sub-
`populations of smoking frequency at baseline (daily, less
`than daily).
`Method 1: Recalled quit attempts, among successful quitters.
`We identified the mean number of quits of successful
`quitters (quit for >1 year) as reported by participants
`who made successful quits in the OTS cohort. We then
`added the number of recalled quit attempts at baseline
`to this figure.
`Formula for Method 1:
`Among smokers who were successful : cumulative number
`of quit attempts observed during the study
`þrecalled number of attempts at baseline=number
`of successful smokers
`This method corresponds to the assumptions that have
`been used previously to calculate the average number of
`quit attempts before quitting successfully using cross-
`sectional
`surveys. We expect
`theoretically that
`this
`method will underestimate the number of quit attempts
`given the known issues with ability to recall quit
`attempts, which will be much more severe over a lifetime
`compared with a 6-month period.13 This method also
`censors the results of unsuccessful smokers, making this
`more precisely stated as an estimate of the number of
`attempts of those who are successful at quitting smoking.
`Method 2: Constant rate assumption. In this method, we
`assumed that the rate of success is constant over indivi-
`duals and that each individual quit attempt is independ-
`ent of previous quit attempts. That is, it assumes that the
`chances of being successful on any one quit attempt do
`not depend on previous attempts to quit, so we can cal-
`culate the number of attempts expected prior to quit-
`ting based only on our estimate of success rate per quit.
`The median and mean attempt numbers are calcu-
`lated from the geometric distribution—the probability
`distribution of the number of Bernoulli trials prior to
`achieving one success, using the formula:
`
`1= p,
`
`where p is the probability of success to derive the mean.
`The probability of long-term success was based on the
`percentage of quit attempts that were successful among
`all quit attempts among attempts observed in the OTS
`survey (170 successful quits out of 3362 attempts, 5.1%)
`and for daily and occasional smokers separately (4.9%
`(n=2930) and 6.0% (n=432), respectively).
`Theoretically, we expect this calculation to underesti-
`mate the number of quit attempts. Quit attempts are
`unlikely to be independent events as probability of success
`decreases with multiple quit attempts (see figure 1).
`Method 3: Variable rate assumption, observed quit success
`rates. In this method, we assumed that the rate of success
`per quit attempt was not independent (in contrast with
`Method 2) but that instead the chance of success varies
`
`Figure 1 Estimated probability of successful quitting (quit
`attempt of longer than 1 year) by quit attempt number in the
`Ontario Tobacco Survey. The top figure includes only
`observed quit attempts, while the bottom figure also includes
`reported quit attempts prior to study entry. Dotted lines
`represent upper and lower CIs. A life table analysis was used
`to calculate probabilities (n=1277).
`
`by previous number of attempts. That is, we recognised
`that the predicted probability of success is less if we
`know that they have tried and failed to quit previously.
`Figure 1 demonstrates that probability of success does
`decrease with increasing number of attempts. We used
`only attempts reported during the period of the study in
`this method.
`To do this, we first calculated the probability of a suc-
`cessful quit per quit attempt observed. We estimated the
`probability of success for each quit attempt using a
`standard life table approach.17 We used quit attempt
`number as the unit of ‘age’ in a life table calculation of
`survival, where the outcome was successful quitting.
`We observed quit attempt ‘age’, that is, the cumulative
`attempt number, and coded whether each attempt was
`successful or unsuccessful. Then, we calculated the fol-
`lowing quantities:
`ni, the number of people who have not quit success-
`fully (>1 year) at quit attempt i (normally the number
`of survivors for that age interval);
`ei, the number of successful quits that occur at that
`quit attempt i;
`
`4
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`
`Open Access
`
`of attempts reported during 18 months of observation
`was 2.0 (SD: 3.15). Among those who did not success-
`fully quit, there were 2.9 attempts (SD: 3.4). Adding all
`previous lifetime quit attempts reported by each smoker
`to their total number of observed attempts (4.3, SD:
`0.25, attempts at baseline) suggests that the successful
`quitter reports an average of 6.3 (SD: 1.4) lifetime quit
`attempts. Successful daily smokers reported a mean of
`6.8 (SD: 1.6) lifetime attempts, while successful occa-
`sional smokers reported a mean of 4.7 (SD: 0.6) lifetime
`attempts (table 3).
`Method 2: Constant rate assumption: Using the estimated
`5.1% success rate per quit attempt found in this popula-
`tion, the geometric mean is then 19.6 quit attempts
`before quitting successfully. When stratified by frequency
`of
`smoking,
`the expected average number of quit
`attempts before quitting successfully would be 20.4 quit
`attempts for daily smokers and 16.7 attempts for occa-
`sional smokers (table 3).
`Method 3: Variable rate assumption, observed quit success
`rates: Using observed quit attempts, the probability of a
`successful quit was highest on the initial quit attempt
`(11% success); the second attempt was much lower at
`5% success, while subsequent attempts were even less
`likely to succeed ( figure 1). Using this distribution of
`quit attempts in the life table analysis, we found that the
`average number of quit attempts expected in order to
`succeed was 29.6 (95% CI 27.6 to 31.6) attempts (area
`under the survival curve, figure 2). The calculation
`when stratified by smoking frequency suggested that the
`average number of attempts for occasional smokers was
`much fewer (table 3).
`Method 4: Life table, with recalled lifetime quit numbers:
`When the lifetime number of recalled quit attempts
`were included to the probability of quitting on a given
`quit attempt, the likelihood for success peaks on the
`fourth to sixth attempt ( figure 1), roughly the average
`of previously recalled quit attempts among the popula-
`tion of
`those attempting to quit, with subsequent
`attempts much less likely to be successful. Using this dis-
`tribution of probability of quitting per quit attempt
`using the life table approach,
`the mean number of
`attempts was 142.0 (95% CI 122.8 to 161.2); daily
`smokers had a mean of 142.3 (95% CI 122.8 to 161.9),
`while occasional smokers had a mean of 21.0 (95% CI
`18.3 to 23.7; table 3).
`
`DISCUSSION
`The average number of quit attempts is likely signifi-
`cantly higher than what is generally communicated to
`smokers. Under what we consider to be the best set of
`assumptions (Method 3: Life Table, Observed Quit
`Rates), this study suggests that a current smoker tries to
`quit on average 30 times or more before successfully
`quitting for 1 year or longer. The life table approach
`within this population-representative longitudinal cohort
`overcomes some of
`the challenges of estimating the
`
`qi, the estimated probability of quitting successfully at
`quit attempt i (calculated as ei/ni);
`pi, the estimated probability of not quitting successfully
`at quit attempt i (calculated as pi=1−qi); and
`si, the estimated probability of not quitting successfully
`from baseline to the end of the quit attempt i (calcu-
`lated as p0×p1×p2×…pi).
`We adjusted for the influence of right censoring (quit
`attempts that are not observed as they occur after the
`period of study observation) using the standard actuarial
`method by calculating ni: subtracting half the number in
`the period that was censored after a quit attempt was
`observed. This calculation provides an estimate of the
`probability of success by quit attempt number, and
`cumulative probability of success. The expected average
`number of quits prior to quitting successfully was then
`obtained by calculating the area under
`the curve
`(equivalent to the restricted mean).20
`We expect that this method will modestly underesti-
`mate the number of quit attempts. Ignoring previous
`quitting history will attribute a greater probability of
`success to earlier rather than later attempts (many of the
`first and second attempts observed are likely to be people
`who are making their third or higher lifetime quit
`attempt), which will produce an overestimate. We also do
`not know what the effect on success rates would be of
`quit attempts made in relatively short succession after a
`failed attempt, compared to attempts made further apart.
`Given that earlier probabilities will have a bigger effect
`on the area under the curve that is used to produce the
`mean, we expect that the overall bias in this method will
`be a relatively modest underestimate, and provide the
`best estimate of the number of quit attempts.
`Method 4: Life table, with recalled lifetime quit numbers. We
`repeated the life table analysis as in Method 3; however,
`for this method, we calculated the probability of success
`per quit attempt on a lifetime basis, by adding the life-
`time recalled quit number at baseline to the observed
`quit attempts under observation in the survey for each
`individual. That is, quit attempt i was calculated as the
`sum of recalled lifetime quit attempt plus the observed
`quit attempt number.
`We expect that this method will overestimate the effect.
`Unlike with Method 3, Method 4 censors the data from
`successful smokers, estimating, in essence, the average
`number of quit attempts among those with difficulty in
`quitting. The method has a similar but opposite issue to
`that of Method 1, recalled life attempts among successful
`smokers. Where Method 1 excludes information from
`people who have not yet quit, underestimating the result,
`Method 4 does not account for people who have already
`quit, overestimating the effect. However, the use of life-
`time recall quit attempt will underestimate the total
`number of quit attempts.
`
`RESULTS
`Method 1: Recalled quit attempts, among successful quitters:
`Among those who successfully quit, the average number
`
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`Table 3 Estimate of the number of quit attempts made prior to successfully quitting for 1 year or longer among 1277 smokers in the Ontario Tobacco Survey for four
`different methods of calculation
`
`Key assumption
`
`Expected direction of bias
`
`Recall of quit attempts over a lifetime
`is valid. Only successful quitters are
`included
`
`Underestimate: only includes successful
`quitters, recall over a lifetime is poor
`
`Expected number of quit
`attempts prior to quitting
`successfully
`Overall
`Daily
`(n=1277)
`(n=1092)
`
`Occasional
`(n=185)
`
`6.3
`
`6.8
`
`4.7
`
`Method
`Method 1
`Recalled quit attempts, among
`successful quitters
`
`Method 2
`Constant rate assumption
`
`Method 3
`Life table, observed quit success rates
`
`Every quit attempt has the same
`chance of success, no matter how
`many previous quit attempts there
`have been
`
`The success rate of quit attempts
`varies by ‘quit attempt age’, as
`observed during the period of the
`study
`
`Underestimate: chance of success decreases by
`number of previous quit attempts
`
`19.6
`
`20.4
`
`16.7
`
`Offsetting: overestimates chance of success on
`quit attempt, may underestimate on subsequent
`attempts
`
`29.6
`
`29.5
`
`11.4
`
`Probable overestimate: recall over a lifetime is
`underestimated, but calculation does not include
`successful quitters who had quit prior to the
`study
`
`142.0
`
`142.3
`
`21.0
`
`Method 4
`Life table, recalled lifetime quit numbers The success rate of quit attempts
`varies by ‘quit attempt age’, as
`observed and recalled
`
`Successful quit attempts were measured as abstinence of 1 year or longer.
`
`6
`
`Chaiton M, et al. BMJ Open 2016;6:e011045. doi:10.1136/bmjopen-2016-011045
`
` on February 27, 2024 by guest. Protected by copyright.
`
`http://bmjopen.bmj.com/
`
`BMJ Open: first published as 10.1136/bmjopen-2016-011045 on 9 June 2016. Downloaded from
`
`JLI Ex. 2017, Page 6 of 9
`
`

`

`BMJ Open: first published as 10.1136/bmjopen-2016-011045 on 9 June 2016. Downloaded from
`
`http://bmjopen.bmj.com/
`
` on February 27, 2024 by guest. Protected by copyright.
`
`Open Access
`
`downside of Method 4 is that it is likely underestimating
`the quit success rates, particularly for the early attempts
`as we were unable to measure the quit success of people
`who quit prior to study entry and who conceivably were
`people who found quitting easier. The implication is
`that the 30-attempt estimate is likely still underestimating
`the true average number of attempts, but the true esti-
`mate is likely lower than that obtained for Method 4.
`The estimate of 30 attempts is consistent with the esti-
`mate of quitting behaviour from Borland et al13 who
`found an annual rate of quit attempts of ∼1 per year.
`Given that most smokers begin smoking as adolescents,
`at an average of one quit per year, if, on average it takes
`30 attempts to quit, we would expect the average smoker
`to quit in their late 40s or early 50s—consistent with
`clinical observations.
`It is important to note that this is a descriptive esti-
`mate, and not a normative one. This has two implica-
`tions. The first is that it is important to consider the
`results as an average of a population, rather than any
`one individual experience. Despite a high number of
`quit attempts needed to quit was found on average in
`this study, many individual smokers are able to quit suc-
`cessfully on relatively few attempts.21 Ashley et al22 sug-
`gested that between 40% and 52% of former smokers
`quit the first time they make a serious attempt to do so.
`This is consistent with the assumption that quit attempts
`are not independent—those who have difficulty quitting
`will need to make many more quit attempts to succeed
`than those who have less difficulty. While many people
`may be able to quit smoking on the first few attempts,
`others may not be able to quit after hundreds of
`attempts. Efforts can also be taken by individuals to
`improve their chances of success, such as using quit aids,
`or receiving counselling.
`The second implication of this is, as a descriptive statis-
`tic, the estimates here in this study describe the experi-
`ence of this population, given the population distribution
`of these factors at the time. To compare the estimate of
`average number of quit attempts from one jurisdiction or
`time period to another may theoretically require stand-
`ardisation of these factors to the Ontario population at
`this time. While there are many factors that affect the
`ability to quit smoking, these estimates can be considered
`accurate for
`this population. The correspondence
`between the estimate found in this study (6.1) to those
`prior estimates that were made under the similar sets of
`assumptions (ie, five to seven attempts)21 suggest that
`there are minimal systematic differences in quitting
`behaviour or recall in this cohort compared to other
`surveys on which previous estimates were based. Thus,
`the differences in the estimates can be attributed primar-
`ily to the different methods rather than the uniqueness
`of the Ontario, Canada population of smokers.
`
`Limitations
`study defined quit attempt as a ‘serious quit
`This
`attempt’
`as
`self-perceived by
`the
`smoker. Other
`
`Figure 2 Absolute survival probability (per cent who have
`not quit successfully) of reported quit attempts of longer than
`1 year during the first 18 months of observation in the Ontario
`Tobacco Survey. The top figure includes only observed quit
`attempts, while the bottom figure also includes reported quit
`attempts prior to study entry. Dotted lines represent upper and
`lower CIs. A life table analysis was used to calculate survival
`probabilities (n=1277).
`
`number of quit attempts it takes a smoker to quit for
`good. Previous estimates of how many quit attempts it
`takes to quit used populations of former smokers exclu-
`sively; these estimates are significantly biased by difficulty
`in recalling past quit attempts, and by not accounting
`for the large number of people who try to quit but who
`are never successful.9 11 12
`We selected Method 3: Life Table, Observed Quit
`Rates as the best set of assumptions as it accounts for
`the biases (lifetime recall,
`independence assumption,
`exclusion of unsuccessful quitters) that affect Method 1
`(Recalled Attempts Among Successful Quitters) and
`Method 2 (Constant Rate Assumption), and conse-
`quently provides a better estimate of
`the average
`number of attempts prior to quitting successfully than
`those two methods. Arguably, Method 4: Life Table,
`Recalled