The transtheoretical model (TTM), also known informally as the stages-of- change model, has been influential in the field of health psychology. The TTM has most frequently been applied to smoking cessation, but has also been applied to many other health-related behaviors. The core of the TTM is the stages-of-change construct, which is a set of five classifications. The first three stages describe people currently engaged in a problem behavior, for example, smoking cigarettes. The precontemplation stage comprises people who are least ready change the problem behavior, the contemplation stage represents an intermediate level of readiness to change, and the preparation stage represents the highest level of readiness to change. There are also two stages defining people who have already changed the problem behavior. The action stage is defined as the first 6 months postchange, and maintenance is defined as sustained change beyond 6 months. The stages-of-change are best understood as intermediate outcomes in the process of long-term behavior change. Stage progression is conceptualized as progress toward behavior change, and ultimately to long-term maintenance of behavior change.
Stages Of Change And The TTM
The stages-of-change construct is only one component of the TTM. Other variables associated with the TTM have been hypothesized as mediators for stage progressions. These variables are known as the processes of change and the pros and cons of smoking. Much research has focused on the relationships between the stages-of-change and these process variables.
The Appeal Of The TTM
The intuitive appeal of the TTM is similar to the appeal of stage models generally. To illustrate, consider the example of smoking cessation. If smokers could be arranged in an ordered set of categories leading to cessation, then interventions could be designed for each category to foster progressive stage movements leading ultimately to cessation and sustained abstinence. In other words, interventions could be matched to stage.
Measuring The Stages
There has been little consistency regarding the measurement of the stages-of-change. Part of this lack of standardization is the inevitable result of defining stages for different problem behaviors. However, even within a specific behavior, such as smoking cessation, many different staging schemes have been employed. Despite the heterogeneity of staging methods, some generalizations can be made. There are essentially two classes of methods for measuring stages. The most common method is a staging algorithm. Staging algorithms rely largely on questionnaire items that require yes-or-no answers to questions regarding intention to change a behavior within fixed time frames. For example, the most recent smoking cessation algorithm defines the precontemplation-stage smokers as those who indicate that they do not intend to quit smoking in the next 6 months. Contemplators, according to the same algorithm, intend to quit in the next 6 months, and either are not seriously thinking about quitting within the next 30 days, had not made at least one 24-hr quit attempt in the last year, or both. Preparation-stage smokers are seriously thinking about quitting in the next 30 days and had at least one 24-hr quit attempt during the last year.
The second method of measuring stages involves continuous scales. Based on this method, each individual receives a “stage score” for each of the stages in the model. Thus, based on this method, an individual can have high stage scores for multiple stages simultaneously.
Empirical Evaluations Of TTM
The TTM is a multifaceted model with a voluminous research literature. Weinstein et al. (1998) propounded four principles by which all stage models, including the TTM, can be evaluated. Next, the TTM is evaluated for each of these four principles.
Principle 1. Stages should consist of qualitatively different and mutually exclusive categories. The stages-of-change, at the conceptual level, comprise a sequence of qualitatively distinct categories. Precontemplators, in theory, are not yet contemplating cessation. Contemplators, in theory, are contemplating cessation, and preparers are, in theory, preparing for a quit attempt. However, theory and measurement cannot be separated. Substantial evidence suggests that the stages-of-change algorithm does not classify smokers into qualitatively different categories. One group of studies pointing to this conclusion is made up of studies employing both the stages-of-change algorithm and alternative measures of readiness to quit within the same sample of smokers. For example, several studies have indicated that large percentages of smokers classified as precontemplators are, in fact, contemplating a quit attempt. Discrepancies were also observed for the contemplation and preparation stages. In addition, researchers have noted the arbitrary distinction between the action and maintenance stages.
Continuous scales for each stage clearly does not conform to Principle 1. This method allows for individuals to have relatively high scores for multiple stages simultaneously. This approach contradicts the idea that stages are mutually exclusive categories.
Principle 2. There should be an ordering of the stage categories. The second principle presented by Weinstein et al. is that stages should follow an ordered sequence. Within the context of smoking cessation, this means that stages should follow a progressive series leading to cessation and maintained abstinence. The stages-of-change algorithm satisfies this requirement. It should be noted, however, that stages are not an invariant sequence. Individuals can skip stages, and regress to earlier stages. Some authors consider the skipping and regressing of stages to be inconsistent with a true stage theory, whereas others do not see this as an important contradiction of stage principles.
Principle 3. There should he similar barriers to change for individuals within each stage. If members of stage are qualitatively similar to one another, then group members should also face similar barriers for making progressive stage movements. This is the rationale underlying the idea of stage-matched interventions. There are two ways to evaluate the TTM with regard to Principle 3: (1) prospective studies of stage transitions and (2) stage-matched intervention studies.
Prospective Studies of Stage Transitions
First, reliable predictors of specific stage transitions should be identified. There have been very few studies addressing this issue. To complicate matters, there are several studies that appear to evaluate the prediction of progressive stage movements, but in fact do not. The first smoking study to use processes of change and pros and cons as predictor variables for stage movements was that of Prochaska et al. (1985). The results of this study were inconsistent, with approximately half of results for individual processes and pros and cons pointing in the hypothesized direction and half pointing in the opposite direction. Surprisingly, only one smoking study since 1985 has tested the capacity of processes of change and pros and cons to predict stage transitions. This study, by Herzog et al. (1999), found processes of change and pros and cons to be ineffective predictors of stage movements.
Stage-Matched Intervention Studies
The record of interventions based on the TTM has been modest. For instance, one prominent smoking cessation study, by Prochaska et al. (1993), compared four interventions: stage-based manuals alone, American Lung Association (ALA) manuals alone, stage-based manuals plus counseling, and stage-based manuals plus individualized computer feedback. Not surprisingly, the multicomponent interventions outperformed the two manuals-only conditions. The two manuals-only conditions (ALA vs. stage) produced comparable results, but the action-oriented ALA manuals produced greater cessation rates for baseline precontemplators than the stage-based manuals. This result runs counter to TTM theorizing, which agues that a major strength of the model lies in its recognition of the particular needs of precontemplators, who are said to be poorly served by standard action-oriented interventions.
Another study, by Quinlan and McCaul (2000), compared stage-matched and stage-mismatched interventions in a sample of precontemplation-stage smokers. The results revealed no advantage for the stage-matched intervention, and moreover revealed a nonsignificant trend in favor of the stage-mismatched condition. Another prominent smoking study, by Aveyard et al. (2001), employed a stage-based intervention for adolescents in Great Britain. The results showed no advantage for the stage-based intervention compared to a control condition.
The TTM has been used to design interventions of a variety of health behaviors (e.g., diet, exercise, and alcohol abuse). Several scholars have conducted reviews of TTM-based interventions for various behaviors. These reviews have come to the same general conclusion: Evidence supporting TTM-based interventions is mixed at best.
Principle 4. There should be different barriers to stage transitions among people in the different stages: If stages are qualitatively different categories, then what helps smokers in one stage should be different than what helps smokers in other stages. Principle 4 would also require that different predictors were significant for different stage transitions. However, no variables have reliably predicted progressive movements out of any of the stages. Likewise, the modest record of stage-matched interventions further indicates that Principle 4 is not satisfied.
The TTM has influenced many researchers and clinicians in their thinking regarding addictions and other health behaviors. At the conceptual and heuristic level, the model has been successful. At the scientific level, however, the TTM has been less of a success.