The transtheoretical model (TTM) questionnaire for smoking cessation: psychometric properties of the Iranian version

BACKGROUND: The transtheoretical model (TTM) is a common framework for studies of smoking cessation. Using the TTM, several instruments were developed to measure to what extent interventions could make changes in people's behavior. The current study aimed to test the validity and reliability of the Persian version of a TTM based questionnaire for smoking cessation in Iran. METHODS: This was a cross-sectional validation study among adult male smokers using the TTM Questionnaire. Backward-forward procedure was applied to translate the questionnaire from English into Persian (the Iranian language). The confirmatory factor analyses were performed to test validity. The internal consistency and stability of the questionnaire was examined using Cronbach's alpha coefficient and Intraclass Correlation Coefficient (ICC). RESULTS: In all 150 male smokers were entered into the study. The mean age of participants was 36.51 ± 7.94 years. The results obtained from confirmatory factor analysis revealed that the data was fit to the model: the goodness of fit index (GFI) = 0.92; the comparative fit index (CFI) = 0.91; the root mean square error of approximation (RMSEA) = 0.065 (95% CI = 0.063-0.067), and the relative chi-square (x²/df) = 1.87, p < 0.001. The Cronbach's alpha ranged from 0.60 to 0.84 indicating an acceptable result. Also Intraclass Correlation of Coefficient (ICC) ranged from 0.61 to 0.83 corresponding to a satisfactory finding. CONCLUSION: The current study provided psychometric evidence for an appropriate, reliable, and valid tool to determine smoking behaviors among Iranian adult smokers. Indeed the findings from this study could be applied in designing smoking cessation interventions in Iran.