Results

SEX DIFFERENCES

For all four waves of data, young men were approximately 10% more likely to report being “non-smokers” than young women. Population estimates from Hill, White, and Segan,4 suggest that slightly more 17-year-old men are non-smokers at school. And Hill and White8 indicate that the difference in proportions of non-smokers between males and females in their early 20s is about 7%. The slightly greater size of the sex difference in the present study may be due to attrition biases. As the patterns of change over time (shown in figure 1) were virtually identical for both sexes, we only report aggregated data.

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Figure 1

Changes in smoking status among school leavers over three six-month intervals.

TRACKING CHANGES IN SMOKING STATUS OVER TIME

Most respondents (62%) used the same smoker type label in each wave, with 57% of the total being “non-smokers” at all four waves (table 2). Thirty-eight per cent changed label on at least one of waves 2 to 4: 16% were non-smokers at wave 1. The other 22% who changed were predominantly occasional or light smokers at wave 1.

Changes in smoker type reported at the four waves over three time intervals are displayed in figure 1. The columns titled “At school”, “3 months after”, “9 months after”, and “15 months after end of school” display the proportion of respondents in each smoker type category for the respective survey waves. The adjacent columns display the interwave changes in smoker type that occurred separately for each smoker type category. The five percentages show the distribution of smoker type responses for the subsequent wave for respondents from a given category on the previous wave.

A description of the non-smoker transitions from wave 1 to wave 2 may clarify interpretation of this figure. In wave 1 (at school), 72% ofall respondents were “non-smokers”. At the next survey period (wave 2), 88% of these respondents were also “non-smokers”, 4% were “ex-smokers”, 7% were “occasional smokers”, and very small numbers were “light” or “heavy smokers”. The 66% of all respondents who were “non-smokers” at wave 2 are made up of the 88% from wave 1 who continued as non-smokers and small numbers who became “non-smokers” from “ex-smoker” and “occasional”. There were very few “light” and no “heavy” smokers who became “non-smokers” (as one would expect).

Focusing on the distribution of responses for each wave, the percentage of “non-smokers” changed the most, dropping from 72% at wave 1 to 65% at wave 4. The number of people in the “occasional” and “light smoker” categories barely changed over the four waves of data. The “ex-smoker” and “heavy smoker” categories gained respondents over the later waves. About 90% of “non-smokers” said that they were “non-smokers” at each subsequent wave.

Across all three transitions, only 40–50% of ex-smokers called themselves “ex-smokers” at the next survey period. A sizeable proportion (30–40%) reported having returned to smoking. Interestingly, about 20% of “ex-smokers” used the label “non-smoker” the next time. This suggests that they re-evaluated the meaning of the label “ex-smoker”.

Fewer than half of the “occasional” smokers retained this label at each subsequent wave (39%, 48%, and 44%), and there were substantial changes in both directions, but more (33–38%) moved to “non-smoker” or “ex-smoker” than to “light” or “heavy” (18–25%).

About half or slightly fewer of the “light smokers” changed their smoking status category at the subsequent survey period; more progressed to “heavy” smoking than to lower categories. More than 70% of “heavy smokers” used the “heavy smoker” label at the next wave. Only small numbers reported being “ex-smokers” in the wave after reporting being a “heavy smoker”, suggesting that few quit in this group.

There were 152 respondents who were “light” or “heavy” smokers at all four waves. At wave 3, 63% of these persistent smokers reported quitting for 24 hours or more in the last year: 11% made one quit attempt, 14% made two, 17% made three or four, and 21% made five or more. The proportion of this group who made quit attempts had dropped to 49% in wave 4: 11% had made one, 15% two, 6% three or four, and 17% made five or more in the past year.

We calculated the analyses in figure 1 again, using the number of cigarettes smoked and number of days in the last week smoked to define the three current smoker categories. Essentially, the same pattern was found.

The Markov chain analyses revealed that the most parsimonious model that fitted the data was a reduced second-order model that specified main effects, two-way interactions for all adjacent time periods, and two-way interactions between waves 1 and 3 and waves 2 and 4. Further, it was assumed that parameter estimates for transitions within the two overlapping sequences were equal—that is, waves 1, 2, and 3 and waves 2, 3, and 4 (G² (176) = 169.57, p = 0.622). This suggests that the same behavioural sequence is repeated over waves 1 to 3 and waves 2 to 4. The parameter estimates for this model are present in table 3 in which waves 1, 2, 3 and waves 2, 3, 4 are represented as waves A, B, C. These estimates are the parameters of the fitted loglinear models, and the size of the estimate indicates the size of the effect. (Readers interested in the details of this analysis are welcome to contact the first author for more information.)

These analyses confirm the suggestions emerging out of an examination of figure 1. They indicate that the most stable smoker-type categories are “non-smoker” and “heavy smoker”, followed by “light smoker”, with the least stable being “ex-smoker” and “occasional smoker”. It also reveals a significant movement from “non-smoker” to “occasional smoker” at the wave A to wave B transition. From figure 1, it is apparent that this is most marked in the wave 1 to wave 2 transition. It is interesting to note that the movement from non-smoker to light smoker has a significant negative parameter, which suggests that non-smokers who are starting to smoke are likely to remain occasional smokers for six months or more before progressing to being light smokers. The double transition interactions—that is, from wave 1 to wave 3 and from wave 2 to wave 4—show that remaining the same type for two successive waves increases the likelihood of remaining that type.

CIGARETTE CONSUMPTION

A small number of “ex-smokers” reported smoking in the past week (14%, 8%, 8%, and 6% for each wave, respectively). Overall, “ex-smokers” had a mean daily cigarette consumption of about a fifth of a cigarette. “Occasional smokers” averaged about one cigarette per day at each time period. “Light smokers” were smoking about four cigarettes a day when still a school student. This number almost doubled to about eight cigarettes 15 months after the end of school. “Heavy smokers” went from smoking an average of about 11 cigarettes a day to 17 a day over the same period. In contrast to the average daily consumption, the maximum daily consumption was relatively stable over the three time periods for each smoker type. Table 4presents the mean daily and maximum daily cigarette consumption among current smokers for “occasional”, “light”, and “heavy” smoker types across all four waves.

Overall, there was a net movement towards a higher level of smoking in terms of self-labelled smoker type and consumption. This trend was particularly evident over the first interval, which included leaving school. There was less transition back to lower levels of smoking.

Discussion

There was moderately high interwave stability in self-labelled smoker type, especially among “non-smokers” and “heavy smokers”. Despite continuity in smoking (or non-smoking) patterns for most people, more than a third (38%) relabelled their type of smoking at some point over the study period. Importantly, about 40% of these people were initially non-smokers; however, we recognise that many of these non-smokers have tried cigarettes before. These findings call into question public health strategies that focus prevention programmes solely on schoolchildren. There is moderate uptake of regular smoking in the first year after leaving school, which corresponds with findings from earlier work.18 19

Furthermore, there is considerable movement between categories. While those who see themselves as “heavy” smokers are likely to remain “heavy” smokers, “light” and “occasional” smokers frequently move categories. Interestingly, there was a significant movement from “non-smoker” to “occasional” smoker, but few people moved from “non-smoker” to “light” smoker over a year. This transition would appear to take longer and perhaps incorporate times of non-smoking, before a period of stable light smoking was reached. Excluding those who remained non-smokers over the four waves, most show changes in their smoking involvement.

Reported consumption rises across waves for the self-described “light” and “heavy” smokers, suggesting that these labels, to some extent, reflect smoking relativities within peer groups. This finding justifies the use of self-referent labels, especially as consumption-based definitions did not produce any notable differences in the pattern of transitions.

Because the heavy smokers were more likely to drop out of the study, the estimated proportion of non-smokers is inflated, so the estimate of transition towards smoking will be slightly inflated. It is also possible that the loss of the heavy smokers has resulted in an underestimate of the stability of that group. Another possible bias is that the mode of survey administration in wave 1 was different from waves 2, 3, and 4. Reporting smoking status in the context of a school classroom may slightly reduce the proportion of people who admitted to smoking, although the work by Stanton et al 31 suggests otherwise. Any such effect would inflate the estimated level of uptake after leaving school.

Average cigarette consumption among “light” and “heavy smokers” increased over 15 months after leaving school. By the end of the study period, the average consumption for “heavy” smokers (approximately 17 cigarettes per day) was only slightly lower than the average consumption for all adult smokers in the same population.8The change in average consumption associated with self-labelled smoker type suggests that young adults have changed their conceptions of what constitutes a “light” or “heavy smoker” over time, perhaps anchoring their self labels around their perceptions of usual consumption among their peers. It is possible that as their peers’ consumption increases, their awareness of this leads to a revision of what “light” and “heavy” mean in terms of daily consumption.

The term “ex-smoker” also seems to carry different connotations for different individuals. The transition to “non-smoker” was common from “ex-smoker”. It seems plausible that this transition occurs among those who smoked experimentally, and after they had stopped completely for some time they reflected that they had never really been a regular smoker. Consistent with this, a similar transition was found from “occasional” smoker to “non-smoker”.

Despite the tendency to progress to higher levels, the fact that few of these school leavers moved rapidly to “light” or “heavy” suggests that there is a window of opportunity to intervene. In this context, we acknowledge that the shifting consumption levels associated with the labels of light and heavy smokers have the effect of reducing the proportions moving across categories as some increase consumption while remaining within the same category. In the absence of an addiction threshold, consumption-based definitions will not necessarily result in a more accurate estimate of those moving to a pattern of continuing regular consumption.

That initiation to smoking is still occurring after leaving school implies that prevention programmes should be extended beyond school. Young adults display a distinct pattern of quit attempts compared with older adults; they attempt to quit more frequently but are also more likely to relapse.33 The initiation and greater instability of use provide a yet-to-be exploited opportunity to intervene with “occasional” and “light” smokers before they become heavily dependent. It is vital to develop programmes appropriately targeted to reverse progression of smoking behaviour and to achieve permanent abstinence among this group of young adults. Such programmes will necessarily be different from prevention programmes focusing on never smoking the first cigarette, and from cessation programmes designed to help motivated self-acknowledged addicts to break their dependencies.