I haven't read through the actual study yet, but I wanted to share this paper: "Current Issues of Usability Characteristics and Usability Testing" by Ayobami, Hector, Hammed. The abstract:
A well given design’s attention to Learnability, Contextuality and Operationability as Usability characteristics issues of software, and information systems generally is an evolving and challenging area in the field of Information systems, and Human Computer Interaction as an area of expertise. The procedure of testing and evaluating usability as quality characteristics in information systems has equally attracted researchers and professionals more in the recent times due to the developers’ attempt to meet the diverse users’ needs in the development of usable information systems. Hence, the paper aims to bring to the limelight; these current issues of usability and usability testing, the trend of the challenges inherent in the usability testing and evaluation process, then suggest the necessary attention that must be provided by subsequent researches in the bid to solve these lingering design research problems.