Translation, Cross-Cultural Adaptation, and Validation of the Thai Version of the Six-Factor Questionnaire for Obesity

Obesity is a global health problem associated with numerous complications. Classification of the psycho-behavioral phenotype of obesity using the 27-item Six-Factor Questionnaire (6-FQ) represents a precision-medicine strategy to improve the effectiveness of obesity counseling. The aim was to conduct a translation and validation study of the Thai version of the 6-FQ, as well as to perform a psychometric evaluation of the instrument. Comprehensibility and item difficulty were assessed using the Item Comprehensibility Index (I-CI) and Item Difficulty Index (I-DI), respectively, following ISPOR principles; results were summarized as the Scale Comprehensibility Index (S-CI) and Scale Difficulty Index (S-DI) for both individuals with obesity (n = 50) and healthcare professionals (HCPs; n = 50). Relevance was evaluated by 50 HCPs using the Item Content Validity Index (I-CVI) and the Scale Content Validity Index (S-CVI). Subsequently, we validated the Thai 6-FQ by assessing its internal consistency and test–retest reliability in 150 individuals with obesity. Exploratory factor analysis (EFA) was used to assess the questionnaire’s construct validity. Six items were modified to enhance cultural relevance. After synthesis and adaptation, individuals with obesity rated the Thai 6-FQ as having excellent comprehensibility and ease of completion (S-CI = 0.91; S-DI = 0.91). HCPs regarded comprehensibility and difficulty as acceptable (S-CI = 0.84; S-DI = 0.88) and judged relevance acceptable (S-CVI = 0.85). The instrument demonstrated excellent internal consistency (Cronbach’s alpha = 0.953) and good test–retest reliability (intraclass correlation coefficient = 0.79). EFA identified five factors that explained 69.19% of the total variance. The Thai translation and cultural adaptation of the 6-FQ preserved the instrument’s original meaning and purpose, supporting its use by individuals with obesity and healthcare professionals in the Thai context. In practice, clinicians can use the score from questionnaire at each visit to monitor progress, and both clinicians and adults with obesity can identify remaining barriers that may contribute to unsuccessful weight reduction.