Aims: The concept of 'stage of change' is widely used by researchers and clinicians in the field of smoking cessation. Our aim was to assess the validity of three staging questionnaires and of the concept of 'stage of change' itself.
Setting and participants: Survey on the Internet in 1025 ever smokers, retest after 8 days in 318 people (31%), follow-up after 32 days in 451 people (44%).
Measurements: Three measures of 'stage of change'.
Findings: Participants (83-93%) were classified in the same stage by all pairs of questionnaires, and 15% changed stage during an interval of 8 days. Including quit attempts in the 'preparation' stage had a large impact on stage distributions, because 18-24% of smokers who had decided to quit in the next 30 days were downgraded to the 'contemplation' stage as they had not made a quit attempt in the previous year. The 'action' stage included 5-7% of occasional smokers. Quit attempts during the past 7 days and 30 days were better predictors of smoking cessation than quit attempts during the past 12 months. Baseline stage and a continuous measure of intention predicted smoking abstinence at follow-up.
Conclusions: These results reflect theoretical and methodological problems with the concept of stage of change. 'Stage' covers four different variables: current behaviour, quit attempts, intention to change and time since quitting. These variables are combined in a somewhat haphazard manner, none of them is measured comprehensively, and intention and time are continuous variables categorized by arbitrary cutpoints. Measuring each of these four variables independently may be preferable to using an incomplete mix of these elements.