Changes in the "stages of change" as outcome measures of a smoking cessation intervention: a randomized controlled trial.

Objective: Employing changes in the "stages of change" as alternative outcome measures of a smoking cessation intervention.

Method: RCT carried out between 2002 and 2004 in Germany with 485 daily cigarette smokers recruited from a general population survey. The intervention was conceptually based on the transtheoretical model, involving individualized feedback letters generated by computerized expert-system technology.

Results: Latent transition analysis was applied to test models for patterns of change, to evaluate stage of change distributions and transitions over time, and to compare the intervention and control group. The patterns of change across three time points could best be described by a model including stability, one-stage regressions, and one-to-four-stage progressions. There were no significant differences between the intervention and control group in the stage of change distributions at each time point or in the amount of stage transitions over time.

Conclusion: The efficacy of the intervention could not be demonstrated. Reasons may include oversampling of smokers who are interested in health-related topics but do not intend to quit, and power problems due to substantial attrition.