Reliability and Validity of the Driver Activity Load Index for Assessing Mental Workload among Drivers in Production Companies

Nowadays, the importance of workload has become more apparent in ergonomic studies. Because workload is part of unsafe situation, it can be the cause of the incident. Therefore, its quantification is important in different occupations. This study was conducted to evaluate the validity and reliability of the DALI questionnaire for assessing the mental load of drivers. The present study is a cross-sectional and descriptive-analytic study. All bus drivers operating in one of the manufacturing companies (100 people) entered the study. In order to evaluate the validity, academic experts and queue experts (Lay Experts) were used. To assess the reliability of the questionnaire, 10 people were selected and the Cronbach's alpha and intra-cluster correlation test were used to test the reliability. Data was analyzed using SPSS version 18 software. The mean (SD) age of participants was 50.8 (8.29) years and the mean (SD) of work experience among drivers was 22.18 (6.22) years. To assess the reliability of the questionnaire, Cronbach's alpha coefficient was used to determine the effective factors in the questionnaire higher than 0.7. Also, intra-cluster correlation coefficient of the questionnaire was higher than 0.7 in all factors affecting the interference factor, which was moderate, which is in the optimum level. Due to the fact that the validity and reliability indices of the questionnaire were all reported to be desirable, the Dali questionnaire (DALI) as a valid and reliable questionnaire in Iran can be used to examine and measure the mental load of drivers.