Assessing stage of change for physical activity: how congruent are parallel methods?

The single-question self-classification Stages of Change scales (SAS) for two modes of physical activity were compared with parallel staging methods. In Study 1, the participants (N = 50) completed SAS in a questionnaire and were then personally interviewed on their physical activity. In four fifths of the cases, SAS indicated the same stage as the interviewer's judgment. In Study 2, a representative survey sample (N = 600) completed both SAS and, in another questionnaire, a three-question algorithm staging instrument (TSQ) constructed for the same target behaviors. About 50% of all participants were placed in the same stage with both instruments. The compatibility rate rose to 80% when the number of stages was reduced from the original eight to five. However, TSQ also accumulated a higher share of cases in the stages with regular action. In both studies, the most obvious sources for incompatible staging were the regularity and time frame of the targeted behavior. Thus, neither SAS nor TSQ is on its own a sufficiently accurate instrument for use in personalized stage-based interventions. TSQ shows no obvious advantages over SAS. In counseling, SAS seems useful in combination with a personal interview.