Usability and User Experience: Design and Evaluation¶

Status: emerging
Last updated: 2026-05-31
Sources: 9781119636113.Ch38.Pdf
Tags: [usability, user-experience, user-centered-design, design-thinking, usability-testing, sus, iterative-design]

Summary¶

Usability is the quality of a system that makes it effective, efficient, and satisfying to use, a term that entered general use in the early 1980s, while user experience (UX) casts a broader net over all experiential, primarily subjective, aspects of use (Lewis & Sauro, 2021). The chapter treats iterative design, user-centred design, design thinking, and service design as the fundamentals of designing for usability and UX. It distinguishes summative evaluation, which measures accomplishment of task goals, from formative evaluation, which detects and eliminates usability problems.

Body¶

Context¶

Lewis and Sauro (2021), in their handbook chapter on usability and user experience, examine how systems should be designed and evaluated to be effective, efficient, and satisfying to use. They treat iterative design, user-centred design, design thinking, and service design as the fundamentals of designing for usability and UX, and distinguish summative from formative evaluation. Within this knowledge base the article is the design-and-evaluation core of the human–computer interaction strand: it builds on the requirements gathered in User Requirements Methods, applies directly to the web context in Website Design And Evaluation, shares the meaning-centred design concern of Representation Design, and connects to inclusive and AI-mediated design in Design For All and Human Centered Design Of Ai.

Key Points¶

Usability and user experience are related but distinct constructs. The term usability came into general use in the early 1980s, alongside related terms such as user friendliness and ease of use (PDF p. 1, orig. p. 972). User experience is a broader concept casting a net over all the experiential aspects of use, primarily subjective experience, drawing on work by Hassenzahl and Tractinsky and others (cited in Lewis & Sauro, 2021). Growing practitioner interest in UX pushed the field beyond narrow task performance toward the full felt quality of interaction (PDF pp. 1–2, orig. pp. 972–973).

Design for usability rests on iteration. Before design iteration can improve a design, there must be a design to iterate; user-centred design (UCD) and design thinking are methods for producing those initial designs, after which iteration improves them, and service design extends the same logic beyond individual products. This makes iterative, user-centred methods the practical core of designing usable systems (PDF pp. 3–4, orig. pp. 974–975).

Usability is defined in two complementary ways. The summative conception concerns accomplishment of global task goals and underlies current standards and the prototypical metrics of effectiveness, efficiency, and satisfaction, with proposals to add attributes such as flexibility and safety (Bevan, 2009, cited in Lewis & Sauro, 2021). The formative conception, traceable to ease-of-use definitions from Chapanis, concerns the detection and elimination of usability problems and supports problem-finding evaluation during design (PDF p. 2, orig. p. 973).

Measurement connects design to evidence. Lewis and Sauro reference the System Usability Scale (SUS) as a widely used measure of perceived usability, illustrating how subjective usability can be quantified for comparison and tracking (PDF p. 3, orig. p. 974).

Conclusion¶

Lewis and Sauro (2021) conclude that usability and UX work rests on iterative, user-centred design coupled to measurable evaluation. Treating usability through both summative metrics and formative problem-finding, and quantifying perceived usability with instruments such as the SUS, keeps usability and UX claims grounded in data rather than assertion.

References¶

Bevan, N. (2009) 'Extending quality in use to provide a framework for usability measurement', in Kurosu, M. (ed.) Human Centered Design, HCII 2009. Heidelberg: Springer-Verlag, pp. 13–22. To be validated.

Lewis, J.R. & Sauro, J. (2021) 'Usability and User Experience: Design and Evaluation', in Salvendy, G. & Karwowski, W. (eds.) Handbook of Human Factors and Ergonomics. 5th edn. Hoboken, NJ: John Wiley & Sons. lewis2021usabilityux

Open Questions¶

How should summative usability metrics be extended to capture the broader, subjective scope of user experience?
When do formative and summative evaluations give conflicting verdicts on the same design, and how should that be resolved?