Failure of post-action stages of the transtheoretical model to predict change in regular physical activity: a multiethnic cohort study.

BACKGROUND: Predicting variation in meeting recommended levels of physical activity is important for public health evaluation.
PURPOSE: The purpose of this study is to determine the predictive value of stages of the Transtheoretical Model (TTM) for classifying people who meet the US Healthy People 2010 guideline for regular physical activity.
METHODS: A cohort (N = 497) from a random, multiethnic sample of 700 adults living in Hawaii was assessed at 6-month intervals three or more times for 2 years. Latent transition analysis was used to classify people according to TTM stages and separately according to whether they met the guideline. The predictive value of pre- vs. post-action stages was then tested.
RESULTS: Stages were more likely to falsely classify people as meeting the guideline than to falsely classify them as not meeting it. Probabilities of predicting 6-month transitions were about 50% for the stable class of meeting the guideline each time and just 25% for transitions between meeting and not meeting the guideline.
CONCLUSION: The TTM post-action stages had limited usefulness in this cohort. Further longitudinal study is needed to determine whether TTM stages can accurately classify transitions from physical inactivity to physical activity below recommended levels.