Validity of processes of change in physical activity among college students in the TIGER study

To test the factorial validity and measurement equivalence/invariance of scales used to measure processes of change derived from the Transtheoretical Model (TTM) applied to physical activity.

Confirmatory factor analysis of questionnaire responses obtained from a diverse sample (N = 1,429) of students enrolled in the Training Interventions and Genetics of Exercise Response (TIGER) Study at the University of Houston during academic years 2004-2005 through 2007-2008. Cohorts of students (N = 1,163) completed the scales at the beginning and end of each Fall semester, permitting longitudinal analysis.

Theoretically and statistically sound models were developed that support the factorial validity of nine of the ten hypothesized 1st-order factors. A structure of nine correlated 1st order factors or a hierarchical structure of those factors subordinate to two correlated 2nd-order factors were each defensible. Multi-group invariance of each model was confirmed across race/ethnicity groups (African American, Hispanic, non-Hispanic White), gender, age, BMI levels, employment status, physical activity level, and study adherence. Longitudinal invariance across the semester was also confirmed.

The scores from the scales provide valid assessments that can be used in observational studies of naturally occurring change or in interventions designed to test the usefulness of TTM processes as mediators of change in physical activity among college students. Item content and factor structure require further evaluation in other samples in order to advance TTM theory applied to physical activity.