This research introduces the concept of transferability into the usability construct and creates the Usability Paradigm for Multiple Device System (UPMDS) to conceptualize and quantify the usability in multiple device scenarios. This study fills the literature gap that no effective method exists in measuring transferability and in quantifying usability in a multiple device context. This study also answers the research questions regarding the impact of task complexity, user experience, and device order on the total usability of the system. Study one follows a systematic approach to develop, validate, and apply a new questionnaire tailored specifically to measure the transferability within a multiple device system. The System Transferability Questionnaire (STQ) is obtained after validation with 15 question items. In a software usability study, the STQ demonstrated excellent internal reliability and validity. Results show that the STQ is effective in capturing four factors regarding transferability, which are transfer experience (TE), overall experience (OE), consistency perception (CP) and functionality perception (FP). Validation results show good convergent, discriminant, criterion and nomonlogical validity. Study two adopts a systematic tool to consolidate usability constructs into a total usability score. The study utilizes principal component analysis (PCA) to determine the weight of the four usability components (satisfaction, transferability, effectiveness, and efficiency), which is used when obtaining the total usability score. Results show slightly different weights for the four components. This quantitative tool can be applied in different usability context in which multiple devices are involved. Usability specialists are encouraged to adjust the tool based on different usability scenarios. Study three investigates the impact of task complexity, user experience, and device order on the total system usability. Results show that the total usability score is not affected by task complexity, user experience or device order. However, lower physical task complexity leads to longer performance time and lower errors from the users. High experienced users have significantly lower errors made in tasks. The machine order also has divergent results. When the mini-lathe machine was used first, users had better transferability results but poorer performance outcomes as compared to when the drill press was used first.

The Online Clothing Reselling Platforms (OCRPs) industry foresees ongoing significant market growth, building upon the expansion it has achieved in recent years. This trend makes it essential to understand how website usability factors affect consumer behaviour and identify practical opportunities for optimization in this specific context of e-commerce. Through empirical research, this study aims to contribute to the existing gap in the literature by analyzing the effect of usability factors on purchase intention and developing a practical usability framework that can guide designers and developers towards the successful implementation of usability factors that facilitates consumer decision-making and purchase intention.  To address the research gap, a mixed-methods multiple case study approach was utilized, combining a heuristic evaluation, a survey of 186 participants, and usability testing with six participants augmented by eye-tracking software and semi-structured interviews. The research was conducted on two key OCRPs, building upon existing knowledge of website usability factors as well as empirical findings.  The results indicate that navigability, content relevance, credibility, and simplicity are positively correlated with increased purchase intention in OCRPs. The study suggests that these four website usability factors should be prioritized when designing and developing these platforms. Based on these findings, a practical usability framework was created to provide designers and developers with actionable insights that can assist them in prioritizing and optimizing website usability to increase purchase intention. The framework lists practical guidelines per usability factor and demonstrates the factors’ interdependence. The framework is designed to further enable the growth of OCRPs by increasing purchase intention through website usability.