What is Usability? A Characterization based on ISO 9241-11 and ISO/IEC 25010

Abstract. According to Brooke [3] “Usability does not exist in anyabsolute sense; it can only be defined with reference to particular con-texts.” That is, one cannot speak of usability without specifying what that particular usability is characterized by. Driven by the feedback ofa reviewer at an international conference, I explore in which way onecan precisely specify the kind of usability they are investigating in agiven setting. Finally, I come up with a formalism that defines usabil-ity as a quintuple comprising the elements level of usability metrics,product, users, goals and context of use. Providing concrete values forthese elements then constitutes the investigated type of usability. Theuse of this formalism is demonstrated in two case studies. 1 Introduction In 2014, I submitted a research paper about a concept called Usability-based SplitTesting 1 to a web engineering conference [10]. My evaluation involved a ques-tionnaire that asked for ratings of different factors of usability based on a novelusability instrument specifically developed for web interfaces [11]. This instru-ment comprises the items