Is contemplation a separate stage of change to precontemplation?

BACKGROUND: Fundamental to a stage-based model of health behavior change is the assumption that there is non-linearity (or discontinuity) in the relationship between predictors and outcomes across stage boundaries. There is, however, little evidence to suggest the stages of the transtheoretical model (TTM) meet this assumption.
PURPOSE: The aim of this study was to extend previous work on discontinuity in prediction to the TTM stage boundary between precontemplation and contemplation, and to test the homogeneity of the contemplation stage of change.
METHOD: Repeated measures design with telephone surveys conducted two weeks apart. Participants were 708 randomly selected smokers, aged 18-40 years, in the precontemplation and contemplation stages of change.
RESULTS: An initial test of the stage boundary between precontemplation and contemplation revealed greater predictive power of a multivariate model in the precontemplation stage. Some evidence of discontinuity in prediction was found within the contemplation stage, between those "open to the possibility" of quitting and those "actually thinking about it." The discontinuity at the TTM boundary was reduced following the exclusion of precontemplators not interested in quitting and when those thinking about quitting within contemplation were also excluded.
CONCLUSION: The stage boundary between precontemplation and contemplation was not strongly supported, and there was weak evidence of a discontinuity within contemplation. The findings question the utility of the current operationalization of the TTM stage boundary.