1995 Paper

Research from the United States suggests that using a course of nicotine patches can facilitate the cessation of smoking. In order to investigate this claim a group of NHS researchers at a local general hospital began a systematic study of smoking cessation. From the hospital records they were able to assemble a list of 90 smokers who agreed to take part in the study. The participants were asked to estimate the number of cigarettes they smoked per day and the researchers allocated the participants to three equally-sized groups whilst controlling, as closely as possible, current smoking rates.

Each participant was given an allocation of patches, one patch had to be worn each day for a period of four weeks. Care was taken to prevent participants from knowing which group they were in. Group 1 were the Placebo group, their patches contained clean pieces of lint. Group 2 were the Patches-Only group, their patches were genuine nicotine patches. Group 3 were the Patches and Counselling group, their patches were genuine nicotine patches and they also received an hourly session every week with a counsellor trained in dealing with the problems associated with smoking cessation.

The number of cigarettes smoked was noted: at the beginning of the trial period (Pre-treatment); at the end of the trial period (Week 4 Post-treatment); and after a further period of six weeks (Week 10 Post-treatment). Summary statistics are presented in Table 1. Unfortunately, due to pressure of work, it was not possible to see all of the participants at the Week 4 Post-treatment stage. All the participants were seen at the Week 10 Post-treatment stage.

Table 1. The mean number of cigarettes smoked per day for each of the three groups tested. (N = the number of participants tested in the associated group at that stage.)

Pre-treatment Wk4 Post-treatment Wk10 Post-treatment
(N = 30)(N = 14)(N = 30)
GROUP 2 36.4 25.1 27.4
(N = 30)(N = 15) (N = 30)
GROUP 3 34.6 24.4 26.2
(N = 30) (N = 12) (N = 30)

Because of the missing data at Week 4, the researchers decided to use two separate analyses of these data. First the data from participants with scores for both stages, Pre-treatment and Week 4 post-treatment, were entered into a two by three split-plot (mixed) design analysis of variance. Group (Group 1, Group 2, Group 3) and testing stage (Pre-treatment vs. Post-treatment) were the factors of interest. This analysis revealed a statistically significant main effect of Group (F(2,38) = 13.49, p < .05), a significant main effect of Testing Stage (F(1,38) = 44.85, p < .05), and significant Testing Stage by Group interaction (F(2,38) = 17.66, p < .05).

Next the data from the Pre-test and Week 10 Post-test stages were analysed in a similar fashion this time using data from all the participants. This analysis revealed, that although the main effect of Testing Stage was statistically significant (P(1,87) = 14.05, p < .05), neither the main effect of Group (F(2,87) = 1.16, p > .05) nor the Testing Stage by Group interaction (F(2,87) = 1.32, p > .05) were significant.

The researchers decided to discard the results of the second set of analyses as they could find nothing of interest to discuss. However, on the basis of the first analysis they concluded that using the nicotine patches was effective in aiding the cessation of smoking.

In a later follow-up study the researchers acted upon more recent work by members of another laboratory. This suggested that the central factor in gauging success in cessation of smoking was not the current smoking rate but the amount of time since the participant started smoking. In this second study the groups were matched for how long they had been smoking instead of current smoking rate. This time just two groups were tested, both generated in a similar quasi-random fashion to that used before. Group 1 had placebo patches, Group 2 nicotine patches. There were 30 participants in each group and all participants were tested pre-treatment and at the end of the trial. Table 2 shows summary statistics of the conditions of interest in Experiment 2.

Table 2. Mean number of cigarettes smoked per day for each of the groups tested.

Pre-treatment Week 4 Post-treatment
GROUP 1 34.6 29.5
GROUP 2 42.2 30.2

These data were now analysed with a two by two split-plot (mixed) design analysis of variance, with Group (Group 1 vs. Group 2) and Testing Stage (Pre-treatment vs. Post-treatment) as the factors of interest. This revealed a statistically significant main effect of Testing Stage (F(1,58) = 16.08, p < .05), and a significant Testing Stage by Group interaction (F(1,58) = 22.05, p < .05). The main effect of Group was not significant (F < 1.0).

From this pattern of results the researchers concluded that nicotine patches aided smoking cessation even when smoking history was controlled. In particular whereas the control group (i.e., Group 1) showed only minimal decline in amount smoked over the testing period, there was a substantial decline in the amount smoked by the experimental group (i.e., Group 2) over the testing period.

To determine the effects of smoking history and initial rate of smoking on the efficacy of nicotine patches, the researchers decided to do a final correlational analysis on the data for the experimental group in the second study. There was a statistically significant correlation between final and original smoking rate (r = 0.66, df = 29) and also between final smoking rate and history of smoking (r = 0.75, df = 29).

On the basis of these correlations the researchers concluded that although there was something of a relationship between the cessation of smoking and the original smoking rate, the critical predictor was the amount of time participants had been smoking before they were treated.

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