Wu Q.Kaewboonchoo O.Ratanasiripong P.Kaewwilai L.Mahidol University2026-05-162026-05-162026-01-01Thai Journal of Public Health Vol.56 No.1 (2026) , 1543-15682697584Xhttps://repository.li.mahidol.ac.th/handle/123456789/116730Objective: Arm lymphedema is a common, lifelong postoperative complication in breast cancer survivors, and adherence to prevention behaviors may help reduce its occurrence. This study aimed to validate the modified questionnaire on adherence to arm lymphedema prevention behaviors and examine the strength of the relationship between constructs of the Health Action Process Approach (HAPA) model and adherence to arm lymphedema prevention behaviors among breast cancer postoperative patients. Methods: A cross-sectional study was conducted from August to November 2024. Exploratory factor analysis (EFA) assessed construct validity, and Cronbach’ s α evaluated reliability. Path analysis using Structural Equation Modelling (SEM) tested the HAPA model and relationships among variables. Results: EFA supported a three-factor structure for the modified questionnaire with an overall Cronbach’ s α of 0.92. In the pre-intentional motivational phase, the path coefficients demonstrated a statistically significant effect of risk perception, outcome expectancy and action self-efficacy on behavioral intention. In the post-intentional volition phase, the path from behavioral intention and coping planning to adherence to arm lymphedema prevention behaviors showed significant effects. However, the effect of coping self-efficacy and action planning on adherence to arm lymphedema prevention behaviors was not significant. Conclusion: The modified questionnaire demonstrated good construct validity and reliability. Risk perception, outcome expectancy and action self-efficacy were key determinants of behavioral intention; behavioral intention and coping planning (excluding coping self-efficacy and action planning) influenced adherence. The results provide a basis for interventions to improve adherence to arm lymphedema prevention behaviors in postoperative breast cancer patients, potentially reducing lymphedema incidence and improving postoperative quality of life.Environmental ScienceAgricultural and Biological SciencesMedicineArticleSCOPUS2-s2.0-10503797909526975866