Introduction to the Highlight Topic "Human Performance at the Computer"

By Gerd Waloszek, SAP User Experience, SAP AG – November 13, 2008

If you ask what the three most important usability factors are, there is a famous answer: performance, performance, performance. This answer definitively highlights the importance of system performance for users. A more refined answer would be: Waiting times come first, then system crashes and errors, and thereafter missing functionality – still giving performance or responsiveness top priority (see What Matters Most?). Having established performance as a crucial characteristic of user interfaces, it is probably long overdue to take a closer look at this topic on the SAP Design Guild. Over the past 12 months, we have published a number of articles on this topic, including some high-level editorials and a number of more detailed design tidbits. This abundance of articles is, of course, not accidental: It reflects my participation in an internal SAP project that investigated performance from the user's point of view.

Some readers may ask about title of the highlight topic. In fact, our internal project was named "perceived performance." However, over time I found that there are many aspects involved, such as system performance, system responsiveness, human performance, perceived performance, optimization of design for performance, and others. How can this variety defined by a common name or framework? In my opinion, the main theme is still a human being that tries to accomplish his or her tasks not only at a computer, but also in close cooperation with it. Thus, both the computer and the human user contribute to the performance and success of a "hybrid system." While "overall performance of the human-computer system" might be a more correct title for this highlight topic, I believe that "human performance at the computer" is catchier and still useful for describing what the majority of the articles are about.


Overview of the Highlight Topic "Human Performance at the Computer"

This highlight topic is structured as follows:

  • Leading article and introduction: The leading article by Ulrich Kreichgauer, who works in SAP User Experience – Infrastructure and is leading the internal SAP performance project, demonstrates both SAP's commitment to delivering software with good performance and SAP UX's determination to consider performance aspects from a user perspective. The introduction – that is, this article – provides an overview of the highlight topic "human performance at the computer" and introduces some key concepts.
  • Introductory articles: Four articles, originally editorials, introduce readers to various aspects of human performance at the computer.
  • Article series "Human Performance at the Computer": This is the core of the highlight topic. It introduces the different performance concepts and covers some of them in detail, including giving advice for improvements.
  • Article series "Waiting at the Computer": This article series supplements the previous one and discusses how users can be given feedback when they have to wait at the computer.
  • Reference section: This section provides useful information. It includes a review of the book GUI Bloopers 2.0 by Jeff Johnson, which is probably the best reference for performance – or better, responsiveness – issues, a glossary, a list of links and references, and a collection of performance analogies.


Introduction to Key Concepts: Performance, Responsiveness, Human Performance, and Perceived Performance

Performance Versus Responsiveness

In the following text, and more or less the whole highlight topic, it is useful to distinguish between a computer system's performance and its responsiveness, even though some performance definitions include the latter. According to Jeff Johnson (2007, 2000), who insists that performance and responsiveness are different, we informally define the two concepts as follows:

  • Performance refers to system speed.
  • Responsiveness refers to how long users have to wait at the computer.

In an ideal world, computers would be lightning fast and there would be no difference between them, because users would not need to wait for the computer at all. In reality however, and despite all the technological advances, waiting times cannot be reduced to zero, and users still have to wait for the computer's response – hence the quest to improve both a system's speed and its reactivity.

Go For a more extended introduction to the concepts, see Human Performance at the Computer – Part 1: Introduction; for more information on system responsiveness, see Human Performance at the Computer – Part 2: Making Applications More Responsive.

Human Performance

As already mentioned, human-computer systems are hybrid systems. Their overall performance is determined not only by the system's speed and responsiveness but also by the performance of the human user. Contrary to system performance, which often deals with times in the milliseconds range, we have to deal with much longer times here, ranging from seconds to hours.

Go For more information about improving human performance, see Human Performance at the Computer – Part 4: On the Way to Performance-Oriented UI Guidelines.

When looking at the three dimensions performance, responsiveness, and human performance, it becomes evident that user interface designers' main task is improving human performance: UI design affects users' performance directly, and performance-oriented guidelines might be one way to find improvements in this area. On the other hand, despite its importance for the actual experiences of users, system performance is completely out of the scope of UI designers. Responsiveness is, however, a field, where technicians and UI designers should cooperate. UI designers can guide technicians: Based on knowledge of how users perceive the performance of a system and how they perform their tasks, UI designers can help developers improve the performance of their applications. They can also evaluate existing systems from a user-centered point of view and suggest areas in which technicians should invest further effort.

System performance, system responsiveness, and human performance, the related questions and their relationship to technology and UI design

Figure 1: System performance, system responsiveness, and human performance, the related questions and their relationship to technology and UI design

Perceived Performance

The term perceived performance means that users judge a system's performance subjectively and often perceive it differently from its objective performance. How users perceive performance and tolerate waiting times depends on a number of factors, such as:

  • The users' observations and their knowledge and resulting expectations derived from prior experiences and system feedback
  • Task-related aspects, such as the users' success and the system's readiness for users to continue their work
  • The system's appropriateness, mediated through continuity and consistency

If developers improve perceived performance, this may actually lead to worse objective performance. But good perceived performance leads to higher user motivation, and thus better overall performance should be expected.

Go For details about perceived performance, see Human Performance at the Computer – Part 3: Perceived Performance. Extensive information on giving feedback is offered in the article series Waiting at the Computer: Busy Indicators and System Feedback.



We hope that the articles in this highlight topic are useful for our visitors and help professionals who have to deal with performance issues gain a quick overview of the field and find information that may be hard to get elsewhere. Admittedly, not too much information about performance issues is out there, and often the scarce sources even cite each other, making it hard to trace information back to its "roots." Our references and links lists may assist in gaining a foothold in this interesting field, which combines technical with psychological considerations, making it particularly interesting and challenging.



The following list contains a number of "basic" references for the topic of human performance at the computer:

  • Alan Cooper, Robert M. Reimann, and Dave Cronin (2007). About Face 3.0: The Essentials of Design. John Wiley & Sons (Chapter: Optimizing for Responsiveness, Accommodating Latency; p.220-221).
  • Jeff Johnson (2007). GUI Bloopers 2.0: Common User Interface Design Don'ts and Do's. Morgan Kaufmann Publishers (Chapter 1: First Principles; Basic Principle 8: Design for Responsiveness; Chapter 7: Responsiveness Bloopers). • Jeff Johnson (2000). GUI Bloopers: Don'ts and Do's for Software Developers and Web Designers. Morgan Kaufmann Publishers (Chapter 1: First Principles; Principle 7: Design for Responsiveness; Chapter 7: Responsiveness Bloopers).
  • Jakob Nielsen (1993). Usability Engineering. San Diego, CA: Academic Press. (Chapter 5; cited by Jeff Johnson). Excerpt in Response Times: The Three Important Limits.
  • Robertson, G., Card, S., and Mackinlay, J. (1989). The Cognitive Co-Processor Architecture for Interactive User Interfaces. Proceedings of the ACM Conference on User Interface Software and Technology (UIST '89), pp 10-18. New York: ACM Press.
  • Robertson, G., Card, S., and Mackinlay, J. (1993). Information Visualization Using 3D Interactive Animation. Communications of the ACM, 36(4): 56-71.
  • Ben Shneiderman & Cathérine Plaisant (2009). Designing the User Interface (5th Edition). Pearson Addison-Wesley (Chapter 10: Quality of Service, p. 405ff).
  • Ben Shneiderman & Cathérine Plaisant (2004). Designing the User Interface (4th Edition). Pearson Addison-Wesley (Chapter 11: Quality of Service, p. 453ff).
Go For more references, see Links and References for Performance; for definitions of performance-related terms see Performance Glossary.


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