The effect of Transtheoretical Model based interventions on smoking cessation

Abstract

The Transtheoretical Model (TTM) proposes that stage matching improves the effectiveness of behaviour change interventions, such as for smoking cessation. It also proposes that standard smoking cessation interventions are matched to the relatively few smokers in the preparation stage and will not assist the majority of smokers, who are in the precontemplation or contemplation stages. This study tested the hypothesis that stage-matched interventions increase movement through the stages relative to interventions not stage-matched. It also tested the hypothesis that the relative effectiveness of stage-matched interventions is greater for people in precontemplation or contemplation (stage-matched for TTM but not for control) than for people in preparation (where both intervention and control were stage-matched). A total of 2471 UK adult smokers were randomised to either control or TTM-based self-help intervention and followed up 12 months after beginning the programme. Content analysis of the intervention and control self-help interventions examined whether control interventions were action-oriented, meaning they emphasised the processes of change relevant for preparation and action. Participants in the TTM arm were slightly more likely to make a positive move in stage, but this was not significant. There was no evidence that the TTM-based intervention was more effective for participants in precontemplation or contemplation than for participants in preparation. There was no evidence that TTM-based interventions were effective in this trial. The control intervention advocated process use appropriate for all stages and was not action-orientated. Stage matching does not explain the modest effects of TTM-based interventions over control interventions observed in some trials. These effects may instead have occurred because TTM-based interventions were more intensive than control interventions.

Introduction

The Transtheoretical Model is a stage-based theory of behaviour change (Prochaska & Velicer, 1997). Stage represents a state in a behaviour change process that is qualitatively psychologically distinct from another state. The stages are precontemplation (not intending to change soon), contemplation (change is being considered but not definitely planned), preparation (behaviour change is imminent), action (behaviour change is occurring), and maintenance (behaviour change has been consolidated). Movement through the stages is hypothesised to be caused by the processes of change (POC), decisional balance, and temptation/self-efficacy. In the TTM, the processes of change are described as the independent variables (Prochaska & Velicer, 1997) and the pros and cons (decisional balance) as mediators of change (Velicer, Rossi, Diclemente, & Prochaska, 1996).

The TTM has spawned much research, often using the constructs such as stage of change to describe a population, and this has become widely accepted. Trials comparing TTM-based interventions to control interventions have produced moderately positive findings, which have been interpreted as disappointing relative to the claims made for the TTM (Riemsma et al., 2003). However, the evidence from these trials is clouded because many of the interventions have often been stage based rather than using all the constructs of the TTM. Furthermore, negative intervention trials may indicate a problem with the formulation of the intervention and not the underlying theory. A smaller body of research has tested specific tenets of the TTM, reviewed in Littell and Girvin (2002) and Sutton (2006). This research has highlighted specific problems with the staging algorithm, which indicates a measurement problem rather than a problem with the underlying theory. The central hypothesis of the TTM is that interventions that encourage the processes of change appropriate for stage would be more effective than those that encourage the use of processes of change inappropriate for a person's stage. There have been few studies that have tested this hypthothesis specifically.

Notwithstanding the limited evidence about the validity of the TTM, Prochaska and Velicer (1997) claimed that the Transtheoretical Model would produce ‘unprecedented effects on entire populations’ (p.47) in changing problematic health behaviour. However, studies using rigorous outcome assessment procedures do not show such large effects (Aveyard et al., 2003, Lawrence et al., 2003, Lennox et al., 2001). We published one study with 6-month prolonged validated abstinence rates being 2.1% in the TTM arm and 1.4% in the control arm measured 12 months from baseline (Aveyard et al., 2003), which is about what would be expected in a population of smokers not motivated to stop. The point prevalence abstinence rates were much higher. Measured in the same way as Prochaska et al., point prevalence abstinence rates were 12.6% in the control arm and 16.0% in the TTM arms. Even though our study enrolled 2471 participants, this difference was not significant, with an odds ratio (95% confidence interval) of 1.33 (0.99–1.80). This effect size is in line with results from a meta-analysis of the effectiveness of tailored self-help interventions of 1.42 (1.26–1.61) (Lancaster & Stead, 2005), but clearly leaves the issue open of whether the intervention was effective or not. The present study examines whether participants in the TTM-based intervention were more likely to move stage towards quitting smoking than the control arm, as recommended by Martin, Velicer, and Fava (1996) and Velicer et al. (1996) because stage movement is a much more common outcome than sustained smoking abstinence and hence the analysis would have greater power.

TTM-based interventions are hypothesised to be more effective than traditional approaches because they target smokers in precontemplation and contemplation (Prochaska & Velicer, 1997). Eighty percent or more of smokers are in these stages (Etter et al., 1997, Velicer et al., 1995). Prochaska and Velicer (1997) state that conventional smoking cessation interventions will not influence these smokers because they are relevant only for smokers in preparation, defined as intending to quit within 28 days. In this study, we examined evidence for this. If this hypothesis is correct, we should see that the effects of stage-based interventions relative to standard interventions are greater for smokers in precontemplation and contemplation than they are for smokers in preparation. In precontemplation and contemplation, standard materials are stage-mismatched, whereas in preparation they are stage-matched.

Two previous studies have provided data on whether this is true (Aveyard et al., 2006, Prochaska et al., 1993). Both studies showed evidence that the greater effectiveness of the TTM-based intervention relative to a standard self-help intervention was because participants in preparation were more likely to stop smoking with the TTM intervention than the standard intervention. In Prochaska et al. (1993) people in precontemplation and contemplation were about 1.6 times more likely to stop smoking than the control when given the TTM-based intervention. In preparation, this ratio of TTM to control was about 2.5. In Aveyard et al. (2006), pregnant smokers in the TTM-based arms were no more likely to quit or move stage than women receiving the standard intervention if they started in precontemplation or contemplation. In all the eight outcomes examined, the relative effect of the TTM-based intervention was greater for women in preparation than it was for women in precontemplation and contemplation, but this difference in relative effect was not significant. In this study, we test the central tenet of the TTM on the importance of stage matching.

The stage match/mismatch studies reviewed rely on the assertion by Prochaska and Velicer (1997) that standard materials are stage appropriate for preparation and action. In this study, we perform content analysis of the materials to examine the assertion that standard self-help materials are stage-matched only for preparation.