What proportion of ever smokers quit? Analysis of information from CAMH from 1996-2016

In the past two decades rates of cigarette smoking have declined; in some countries the declines have been dramatic [1-3]. “In the United States, more than three out of every fi ve adults who were ever cigarette smokers have quit smoking” [4]. Several possible explanations for the declines can be put forth: increased information about the adverse health effects of cigarette smoking [5,6] and exposure to environmental tobacco smoke [7], fewer public places where smoking is permitted, often supported by legislative restriction [8,9], lower levels of smoking initiation and past year use among adolescents and teens [9], increased availability of smoking cessation aids, although less than one-third of people who quit Abstract

Information is available about rates of quitting smoking among people who have been regular smokers. Some recent evidence indicates that the rate of quitting in the general population and among ever smokers may have increased in the past two decades [1,12].
As a result, there are fewer cigarette smokers and more individuals who report quitting in the general population than in the past [13]. However, what is not known is whether the rates of quitting among those who have ever been regular or occasional smokers have remained stable over an extended period of time or whether the rate of quitting among ever smokers has increased over time. In addition, little information is available on whether there have been changes in quitting over time among those with different demographic characteristics, such as age and sex. The purpose of this research is to examine trends in the rates of reported quitting (for more than twelve months) among regular and occasional smokers in the Province of Ontario for over twenty years. In addition, we examine trends in the rates of quitters among the general population, including those who have smoked and the population overall, and examine the trends for males and females, and for different age groups.  The sampling procedure changed in 2017 from a "landline/ list-assisted" sampling frame to a "dual-frame" sampling (landline + cell phone sampling frame).

Methods
The design employs a two-stage probability selection procedure. Within each regional stratum, a random sample of telephone numbers is selected with equal probability in the fi rst stage of selection (i.e., households). Within households of selected telephone numbers, one respondent aged 18 years or older who could complete the interview in English is usually selected according to the last birthday method. For each calendar year, the monthly or quarterly samples were combined to provide a single annual dataset. Across years, response rates ranged from 69% to 41%, [14], which is consistent with other surveys of this nature [15,16]. The data were weighted to adjust for varying selection probabilities, regional representation and a fi nal post-stratifi cation adjustment to restore the age by gender distribution based on the most recently available census and (tc5) "How long ago was it that you last smoked?" Current smoking is defi ned as someone who responded "daily smoker" or 1) responded "occasional smoker", 2) has smoked over 100 cigarettes in lifetime, and 3) has smoked within the past 30 days. Former smoking was measured in the following way: the individual responds that they are smoking "not at all" but 1) have smoked 100 cigarettes in their lifetime and 2) have not smoked for the past year or more. Duration of quitting beyond the one year point was not taken into account in the analysis. categories: 1) those who report they are occasional smokers but have not smoked 100 cigarettes, 2) those who say that they are occasional smokers, have smoked 100 or more cigarettes but have not smoked in the past month, and 3) those whose respond they are not currently smoking, but have smoked more than 100 more cigarettes and have quit less than 1 year ago.
Because of the skip patterns in the surveys, it may be diffi cult to accurately categorize everyone. Finally, some individuals did not respond or refused to respond to at least one of the three smoking questions so their response was counted as Missing.
For each year from 1996 to 2016, weighted frequencies and proportions of both all participants and ever smokers were calculated. Weighted linear regression analyses of the percentages of former smokers were calculated for the years 1996 through 2016, for (1) all ever smokers and (2) for ever smokers by sex and age group categories [17].

Results
In Table 2, we present the frequency and percentages of each smoking category over the years 1996 to 2016 (with the denominator being the total sample). In Table 3, we restrict our analyses to ever smokers and we present the prevalence of current and former smokers among ever smokers (current and former smokers). Figure 1 shows a plot of former smokers, as a percentage of ever smokers, and the linear regression line over years. This line has slope 1.125 and is statistically signifi cant (p<0.001). Thus, the overall rate of former smoking is increasing signifi cantly over time. Figure 2 shows the plot of former smokers separately for males and females. The slope for the males is 0.959 (increase in percentage per year) and for the females is 1.271; these slopes are signifi cantly different (p= 0.0049), that is, although the rate of former smokers for ever smokers has been increasing over time, compared to men, the rate of former smokersfor women is signifi cantly greater.  Current smokers: Individuals who smoke cigarettes daily or (1) smoke occasionally, (2) reported smoking 100 or more cigarettes in their lifetime and (3) smoked during the past 30 days.

Quitters / Former smokers:
Individuals who reported not currently smoking but have smoked 100 or more cigarettes in their lifetime, and have not smoked at all in the past year or longer; Ever smokers: Current Smokers plus Quitters. Individuals who do not fi t into one of the two categories of current smoker and quitter are not included in the denominator when quitting among ever smokers is calculated.
Never smokers: Individuals who responded "not at all" when asked about current smoking and indicated that they had not smoked 100 cigarettes in their lifetime; Others: Individuals who do not fi t into one of the clearly defi ned categories: This group includes those who report they are occasional smokers but have not smoked 100 cigarettes, those who are occasional smokers who have smoked 100 or more cigarettes but have not smoked in the past month, and those who say that they are not smoking currently, but report that they have smoked more than 100 cigarettes but quit less than 1 year ago.
Missing: Individuals who did not respond or refused to respond to at least one of the three smoking questions. that of the baseline level, 55+ (p= 0.0148). The rate of former smokers is greatest for the oldest group and smallest for the youngest group. In addition, although the increase in the rate is the same for the youngest and oldest groups, for the middle age group, the increase is about twice that of the other two.

Discussion
It is interesting to note that the rate of former smoking among the general population has remained stable over time, while the rate of former smoking among ever smokers has increased dramatically over time. The difference in the percentages is due to the fact that there has been a marked decline in the per cent of the population who report ever smoking. Possible explanations for the trend in ever smokers is that public health messages and quit smoking strategies have become more accessible and available over time. Quit smoking messages focus on the benefi ts of quitting, such as avoidance of the detrimental health effects of continued smoking and provide information on available pharmacological ways to     Age is related overall to quitting among ever smokers and could be explained by age related increasing risk of disease among long term smokers [18]. Collection of qualitative information about quitting and aging could provide the basis for interventions and messaging. What is unclear at this point is how much the availability of alternative types of tobacco use are impacting the behaviour of younger smokers [19][20][21].
In the future, questions concerning substitution of products contingent upon quitting would certainly be in order. One interesting fi nding from CAMH 2013-2016 is that over 50% of individuals in all three age groups who are categorized as quitters report using e cigarettes in the past 30 days (unpublished fi ndings). In addition, there is more reported past 30-day e cigarette use among quitters than among current smokers in all three age groups.
There are some limitations to the fi ndings that should be