Intention-behavior relationship based on epidemiologic indices: an application to physical activity.

PURPOSE

This article examines the usefulness of epidemiologic indices in furthering the understanding of the intention-behavior relationship in the field of physical activity.

DESIGN

Six prospective data sets of physical activity were used.

SETTING

The United Kingdom and Canada in various settings (school, workplace).

SUBJECTS

Different segments of the population (students, employees).

MEASURES

Intention at baseline and behavior at follow-up, both assessed by means of questionnaires.

ANALYSIS

Intention and behavior were dichotomized to create a 2 x 2 table; this allowed us to compute four standard epidemiologic indices: sensitivity, specificity, positive predictive value (PV+), and negative predictive value (PV-).

RESULTS

Sensitivity was 86.3%, which reflected the high sensitivity of intention for exercising, i.e., active individuals were very likely to hold a positive intention. Specificity was 49.5%, which suggested that a significant number of inactive individuals held a positive intention. With respect to predictive values, a low intention was a very good predictor of being inactive (PV- = 88.1%), whereas a positive intention was a moderate predictor of being active (PV+ = 45.5%).

CONCLUSION

These results indicate that intention is a moderate predictor of behavior and that the gap between intention and behavior is caused by high intenders not taking action. Health promotion programs would benefit to target factors that moderate the intention-behavior relationship.