Usability

Definition and delimitation

Usability, usually translated as “suitability for use” or “user-friendly design”, describes the quality of interaction between users and a system, software or product.

The most common definition of usability comes from the DIN EN ISO 9241-11 standard:

“Usability is the extent to which a system, product or service can be used by specified users in a specified context of use to achieve specified goals effectively, efficiently and satisfactorily.”

This means that usability cannot be assessed or described in isolation from a context of use, but requires precise knowledge of the respective target group and their tasks and requirements: for example, image editing software that is used in a private context may not be suitable for professional photographers and vice versa.

The definition also specifies three central criteria:

• Effectiveness: how accurately and completely can users fulfill their tasks and achieve their goals?
• Efficiency: What is the cost-benefit ratio?
• Satisfaction: Is the use of the system free of impairments and do the users have a positive attitude towards it?

The term user experience (UX) goes beyond usability and also includes the emotional experience and aesthetic evaluation of a system or product and also refers not only to the actual use, but also the period before and after. DIN 9241-210 defines user experience as follows: “A person’s perceptions and reactions resulting from the actual and/or expected use of a product, system or service.”

Since the 2020 update, DIN EN ISO 9241-110 [1] also includes the similarly defined user engagement as a newly introduced interaction principle.

The term accessibility should also be mentioned here. The focus here is on the accessibility of a system or product for as many people as possible, including those with various impairments. The internationally recognized Web Content Accessibility Guidelines (WCAG) set standards for improving digital accessibility based on the principles of perceptibility, usability, comprehensibility and robustness. Taking accessibility criteria into account can also contribute to good usability and improve the user experience. Conversely, improvements in usability, such as a simplified user interface, can increase accessibility by making it easier for people with disabilities to use.

The term usability is viewed critically in scientific discourse. It is often associated with a misleading view of usability (see also 4.) and should be avoided. It is not about being “nice” to the user, but about ensuring high product quality.

History

Early computer systems were typically reserved for experts with the appropriate programming skills. Nevertheless, the first ideas and visions of interactive systems in which people could influence the system’s behavior at runtime (unlike batch processing) in order to be able to process complex problems whose solution path could not be precisely predetermined can be found very early on. The model for such dynamic human-computer interaction was communication between people early on. Pioneers in this field were, for example, J. C. R. Licklider, head of ARPA, a US military research facility, who thought early on about optimized cooperation between man and machine, or Vannevar Bush, technology advisor to US President Roosevelt and mastermind of the Word Wide Web and modern hypertext systems, who presented “Memex” in 1945, a hypothetical machine for structuring information, which was intended to enable a personalized library for the individual structuring of information through references, notes and annotations, see [2].

In the 1960s and 1970s, the first window-based and graphical user interfaces were introduced, such as the NLS system by Douglas Engelbart, the inventor of the computer mouse. Such research work led to the development of commercial products in the early 1980s, such as XEROX Star and Apple Macintosh with graphical user interfaces and an orientation towards objects and concepts from everyday office life (desk metaphor) in order to simplify use. The era of personal computing began: it became important that computers could also be operated by non-computer scientists, especially office workers. The increasing spread of computer applications in the private sector also contributed to this. Software ergonomics and Human Computer Interaction (HCI) developed as a field of research, see [2], [3].

The spread of the Internet and later the development of mobile devices brought with it new fields of application and design requirements for usable web and mobile applications.

Since the end of the 1990s, the aesthetic design of software and digital applications and the positive user experience (joy of use) have also come to the fore, cf. e.g. [4], which ultimately led to the concept of user experience presented above.

Application and examples

A usable design is important in practically all areas of the development of technical and interactive systems. The realization that it pays off to invest in a product that is easy to use and to accept a certain amount of additional development work is becoming increasingly widespread. Nevertheless, usability is particularly important in areas where people decide for themselves which applications they want to use (i.e. mainly in the private sphere) and where there are numerous options available (e.g. web-based or mobile applications, for which there are usually alternatives if a product is not easy to use). However, it is also worth investing in good usability for work-related software, as this has a positive impact on employee satisfaction and productivity.

Some examples of fields of application are listed below:

• Websites and mobile applications: On the web as well as in mobile applications, alternative products are often just a click away and there is a high risk that users will quickly drop out if they encounter problems. Good self-description capability, clear navigation and fast loading times are therefore particularly important in this area. The aesthetic design and user experience also play a special role.
• Work-related software: Operating systems, office software and other specialized programs often lag behind in terms of usability. Users usually have little choice here, and in the case of applications for a very specific usage context, the focus is usually on the range of functions. Increasingly, however, good usability and user experience are also being taken into account for work-related software, as users are familiar with and expect corresponding standards from privately used applications.
• Technical devices: Usability is also important for the design of physical products and classic design principles can be applied to them. In addition, there are aspects of hardware ergonomics, such as haptics.
• Safety-critical systems: Usability is particularly important in the design of safety-relevant or medical systems. Here, in addition to the usual design aspects, it is particularly important that users are able to operate the system without errors even in stressful situations and that errors or critical system states can be quickly identified and rectified.

Criticism and problems

Usability is still sometimes misunderstood as a purely decorative component. This is also reflected in the sometimes still prevalent division of labor between designers and developers, whereby the latter are responsible for the functional and the former for the visual design and do not always work hand in hand. However, as mentioned at the beginning, good usability requires precise knowledge of the context of use and the target group. Usability therefore means not only product quality, but also process quality, in that the tasks, prerequisites and requirements of the users are precisely analyzed during the development process by applying usability engineering methods. An appealing visual design cannot compensate for problems resulting from a lack of knowledge of the context of use.

The inclusion of usability aspects in the development process, such as an in-depth requirements analysis or the implementation of usability evaluations, requires additional resources. However, it is increasingly being recognized that good usability can also represent a competitive advantage and contribute to higher productivity, error reduction and customer satisfaction.

Research

Research in the field of human-computer interaction is highly interdisciplinary and combines findings from computer science, design, psychology, cognitive science, work and organizational sciences as well as sociology or education, for example, when it comes to researching the social impact of technology use or the use of digital media in teaching and learning. HCI research is therefore also characterized by a wide range of different methods. Laboratory and experimental studies can be found alongside field studies, quantitative and qualitative approaches. Design research, i.e. (prototype) system development as a research approach, also plays a major role.

Human-computer interaction as an interdisciplinary field of research (cf. [5])

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