Assessment of validity and reliability of Persian version of System Usability Scale (SUS) for traffic signs

Usability is the extent to which a system, product or service can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use. Increased public awareness of the usability issues has caused that usability plays an important role in production. Brooke’s SUS is one of the most used tool for measuring usability. Yet, the Persian translation of this tool has not been available to Iranian researchers, and therefore this study has been conducted in order to provide the Persian translation of it and measure its psychometric validation in assessing usability of traffic signs.
Modified version of SUS by Annie(2011) was translated using Backward-Forward method of translation. For measuring validity of the questionnaire the opinions of 10 experts in related field were used. Content Validity Ratio (CVR) was measured based on Lawshi method and Content Validity Index (CVI) was measured based on Waltz and Basel method. The questionnaire content validity index was also calculated.There is 10 items in SUS for assessing usability of each traffic sign, therefore for assessing usability of 20 selected traffic signs, a 200 items questionnaire was developed. Questionnaires were distributed among 50 staff of Iran University of Medical Sciences. Cronbach’s α was used was used to measure the reliability of the questionnaire. Stability of questionnaire was calculated by using test – retest and intra-cluster correlation index.
All the items in SUS showed a high level of CVR and all items were accepted. CVI of all items were above the acceptable level of 0.79 . Content validity index was equal to 0.927. Cronbach’s α was equal to 0.965, and inter-cluster correlation index was equal to 0.993.
The Persian version of SUS is a reliable tool for measuring usability level and showed a high level of validity and reliability and can be used for future researches in the field of usability.