Objectives: The stages of change component of the transtheoretical model have been applied to safe sex behaviours in cross-sectional analyses, but have not yet been subject to prospective analysis. It was predicted that: (a) cross-sectional analyses would demonstrate good discrimination between the stages of change; (b) prospective analyses would allow for the identification of predictors of stage transitions; and (c) implementation intentions would explain progression from the preparation stage.
Design: This study employed an experimental longitudinal design. Participants were randomly assigned to the experimental (implementation intention) or control conditions and completed questionnaires at baseline and at 2-month follow-up.
Methods: Five hundred and twenty-five adolescents who were broadly representative of the UK population completed questionnaires at baseline and follow-up (N=393) measuring: demographic variables; stage of change; theory of planned behaviour constructs; anticipated regret; and moral norm in relation to condom-carrying behaviour. The experimental condition completed a self-generated implementation intention to carry condoms at the end of the baseline questionnaire.
Results: Discriminant function analyses indicated that the stages of change could be accurately discriminated from one another cross-sectionally and that, longitudinally, the measured variables were able to predict transitions between most stages. Implementation intentions caused people to progress from the preparation stage.
Conclusions: Transitions between most stages were reliably predicted, thereby providing potential targets for intervention. The brief implementation intention intervention was effective and could easily be utilized and expanded to encompass a broader range of sexual health behaviours.