Translation, cultural adaptation, and psychometric evaluation of the NASA-TLX questionnaire among various occupational groups of Persian speakers.

Abstract

Mental workload is a critical determinant of employee performance, safety, and well-being. The NASA Task Load Index (NASA-TLX) is one of the most widely used instruments for assessing perceived mental workload; however, a validated Persian version for occupational settings has been lacking. This study aimed to translate, culturally adapt, and evaluate the psychometric properties of the NASA-TLX in a Persian-speaking occupational population. The original NASA-TLX was translated and culturally adapted following established guidelines. Content validity was evaluated using the Content Validity Index (CVI) and modified Kappa coefficients. Structural validity was assessed using exploratory factor analysis, and known-groups validity was examined by comparing three occupational groups. Internal consistency and test-retest reliability were evaluated using Cronbach's alpha and intraclass correlation coefficients (ICCs). Agreement between the weighted and unweighted scoring methods was assessed using Pearson's correlation and Bland-Altman analysis. A total of 605 participants completed the Persian NASA-TLX. Content validity was excellent (I-CVI range: 0.88-1.00; S-CVI/Ave: 0.92; modified Kappa: 0.87-1.00). Exploratory factor analysis supported a unidimensional structure, explaining 73.1% of the total variance. Known-groups analysis demonstrated significant differences in perceived workload across occupational groups. Internal consistency was excellent (α = 0.922), and test-retest reliability was high (ICC = 0.841-0.913). Bland-Altman analysis demonstrated acceptable agreement while identifying a systematic difference between the two scoring methods. The Persian NASA-TLX provides a valid and reliable instrument for assessing perceived mental workload in Persian-speaking occupational settings. The findings support its use for ergonomic assessment, occupational research, and cross-cultural workload comparisons. The unweighted scoring method may be suitable for routine field applications, whereas the weighted method remains preferable when a more detailed workload profile is required.