Supplementary Material for: Translation, cross-cultural adaptation, and validation of the Swallowing Outcomes After Laryngectomy (SOAL) questionnaire in Serbian

Introduction: Total laryngectomy (TL) is a standard curative procedure for advanced laryngeal and hypopharyngeal malignancies. A common but often underestimated complication post-TL is oropharyngeal dysphagia, which can lead to weight loss, nutritional deficiencies, and reduced quality of life. The Swallowing Outcomes After Laryngectomy (SOAL) questionnaire is a 17-item self-administered tool designed to assess swallowing function in TL patients. This study aimed to translate, culturally adapt, and validate the SOAL questionnaire for use in Serbian-speaking populations. Methods: A standardized forward-backward translation methodology was employed to adapt the SOAL questionnaire into Serbian. The study included 136 participants: 69 post-TL patients and 67 healthy controls. Psychometric properties of the Serbian version were evaluated, including construct validity through exploratory factor analysis, internal consistency using Cronbach’s alpha, and reliability through item-total correlations. Results: Significant differences were observed in total SOAL scores between TL patients (mean 6.33 ± 5.19) and controls (mean 0 ± 0; p < 0.001), confirming discriminant validity. Exploratory factor analysis revealed five components, illustrating the multidimensional nature of swallowing issues post-TL. The Serbian SOAL demonstrated high internal consistency (Cronbach’s alpha = 0.849) and strong item-total correlations, supporting the reliability of the instrument. Conclusion: The Serbian version of the SOAL questionnaire is a valid and reliable tool for evaluating swallowing outcomes in patients following total laryngectomy. Its strong psychometric properties support its use in clinical and research settings for Serbian-speaking populations.