Cross-Cultural Adaptation and Psychometric Properties of the SF-8 Questionnaire in Tanzanian Swahili for Injury Population

Background: There is a lack of tools to screen for health-related quality of life (HRQoL) in acute injury patients, despite the critical need for having a good understanding of the characteristics of mental health during the rehabilitation process. The SF-8 instrument, a shorter version of the SF-36, is the most widely used patient-based assessment of HRQoL. The aim of this research is to adapt the psychometric properties of the SF-8 to Swahili. Methods: This study is a secondary data analysis of previously collected and psychometric evaluation of the culturally adapted and translated SF-8. A cross-cultural adaptation committee carried out the process of translation to provide validity evidence based on test content. Confirmatory factor analysis was used to test the internal structure-based evidence. The validity based on relation to other variables (discriminant evidence) was tested using polychoric correlation with PHQ-2 (Patient Health Questionnaire-2). The reliability was tested using Cronbach's alpha, Omega McDonald, and Composite Reliability. Results: 1434 adults who suffered an acute injury and presented to the emergency department between April 2018 and August 2020 were included in the study. The instrument demonstrated language clarity and domain coherence, showing validity evidence based on test content. The CFA (Confirmatory Factor Analysis) analysis showed good fit indices for both models (one- and two-factor models) of the SF-8. The discriminant evidence showed that SF-8 scores correlate strongly with the PHQ-2 instrument. These results supported the validity evidence in relation to other variables. All analyses of reliability were considered adequate with values above 0.90 for both models of the SF-8. Conclusions: The results show that the SF-8 instrument can provide relevant information about the health-related quality of life of acute injury patients, and allow practitioners to gain a better understanding of mental health, improving the treatment and follow-up of injury patients within Tanzanian culture.