Estimating Construct Validity of Four Measures of Readiness to Exercise

Abstract

Exercise stage of change (ESOC), or motivational readiness to exercise, is a key component of adopting regular exercise. Because ESOC stage classification may vary according to the measure used, a challenge is to accurately measure ESOC. At least 15 or more self-report ESOC measures are referred to in the literature, many having limited validity testing. No study was found that systematically compared ESOC measures and estimated their construct validity in the same sample. Prochaska's stage of change model was the framework for this study. PURPOSE: The purpose of this study was to determine agreement among ESOC classifications using three instruments and a recently developed face-to-face structured interview, and to estimate construct validity of ESOC measures. The ESOC instruments (scales) were of three different, but commonly used formats and included Marcus' truefalse, Cardinal's ladder, and Nigg and Riebe's single question with five answer choices. METHODS: Using a one-group, correlational design and convenience sampling, healthy adults (n = 95), aged 19 to 62, completed ESOC measures in random order, and scales on exercise self-efficacy, decisional balance pros and cons, experiential and behavioral processes of change, and exercise performance. RESULTS: Using weighted kappas, most agreement was found between classifications using scale ladder and scale 5-answer choice (kw = 0.854, p < 0.01), and between interview and scale ladder (kw = 0.852, p < 0.01). To estimate construct validity, validation hypotheses were used. There was 100% agreement in ESOC classification across all four measures in 61.1% of subjects. Across all four measures, mean exercise performance was higher (p < 0.05) in maintenance, and exercise selfefficacy and behavioral processes of change were significant predictors of ESOC. When t-scores from validation measures were graphed, only patterns from scale true false were most like those expected based on the literature. CONCLUSIONS: Agreement between measures was at least "substantial." Although overall, the true false ESOC measure most closely met the validation hypotheses, we cannot conclude based on the study findings that true false is substantially superior to the other measures in evaluating ESOC.