Approximately, 45% reported quitting smoking, with a mean age of 40 years [range 7–89 years]. Men were almost as likely as women to report quitting while those endorsing Caucasian ethnicity were more likely than other ethnic groups to report quitting as were those participating from the West Coast census region. Those living below the poverty line at the time of interviews were less likely to quit. Sample characteristics are presented for the those with a lifetime history of smoking a 100+ cigarettes, stratified as those who quit/remained smoke-free for the past 12 months (N=7,750) and those who smoked in the past 12 months (N=10,167) in . Results from survival analyses conducted in the four age groups are shown in .
Table 1 Prevalence of socio-demographic and psychiatric correlates in those who smoked 100 or more cigarettes, lifetime, in the National Epidemiological Survey of Alcohol and Related Conditions (N=17,919), stratified by their current smoking status and their (more ...)
Hazards ratios with their 95% upper and lower confidence limits, in each of the 4 age-groups, showing association between socio-demographic and psychiatric correlates and quitting cigarette smoking (last cigarette smoked prior to the past 12 months).
3.2.1 Young adults (18–31 years)
In these individuals, the prevalence of quitting smoking was 12% (median quitting age of 22 years). Those living on the West Coast were more likely to quit smoking as were those living above the poverty line. A prior history of nicotine dependence was associated with a lower likelihood of quitting smoking whereas those with specific phobias were at increased hazards for quitting. No violations of the proportional hazards assumptions were noted in this age group.
3.2.2 Intermediate-aged adults (32–43 years)
Approximately 29% of those in this age group had quit smoking (mean quitting age of 28 years). In this group, in addition to Caucasian ethnicity and poverty, both of which predicted a reduced hazard of quitting, a prior history of nicotine dependence, panic disorder and generalized anxiety disorder were associated with lower hazards of quitting. Social phobia was associated with an increased likelihood of smoking cessation. For panic disorder and Caucasian ethnicity, a violation of the proportional hazards assumption was noted. Introducing interactions between each of these measures and quitting smoking after 30 years of age satisfied the assumption, although only the interaction with panic disorder was significant [Hazard ratio 3.14]. This suggests a non-linear relationship such that individuals with panic disorder were more likely to quit smoking after 30 years of age, although this is likely associated with mean onset age of panic disorders being middle-adulthood.
3.2.3 Middle-aged adults (44–60 years)
Quitting was most common in this age group (47%, mean age 36 years). A number of risk factors were associated with a reduced likelihood of quitting, including poverty, Caucasian ethnicity, a family history of alcohol/drug problems, nicotine dependence, major depressive disorder, generalized anxiety disorder, social phobia and alcohol abuse/dependence. Living on the West Coast was associated with an increased likelihood of quitting. Significant (p < 0.01) violations of proportional hazards were noted for nicotine dependence, major depressive disorder, generalized anxiety disorder and alcohol abuse/dependence. Graphical tests of the violations demonstrated that for major depressive disorder, nicotine dependence and generalized anxiety disorder, occurrence of the psychiatric disorder was associated with delayed age of quitting (after 35 years of age). For alcohol abuse/dependence, however, there was a significant increase in failure to quit in early adulthood (18–20 years) and lower risk associated with quitting smoking between 35–60 years of age.
3.2.4 Older adults (61–99 years)
About 72% of those in this age-group had quit smoking (mean quitting age of 48 years). Factors associated with quitting in this age group were identical to those for individuals aged 44–60 years, with the exception of generalized anxiety disorder and social phobia which were unrelated to cessation in this age group. Violations of the proportional hazards assumption were noted for major depressive disorder and alcohol abuse/dependence. Major depressive disorder was a significantly better predictor of inability to quit when the participants were under 50 years of age. As in the middle-aged adults, the risks associated with alcohol dependence were significantly greater in early adulthood and diminished dramatically after 35 years of age.