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Response Time: Eight Seconds, Plus or Minus Two

People hate to wait.

Slow response times and difficult navigation are the most common complaints of Internet users. After waiting past a certain "attention threshold," users bail out to look for a faster site. Of course, exactly where that threshold is depends on many factors. How compelling is the experience? Is there effective feedback? This chapter explores the psychology of delay in order to discover why we are so impatient, and how fast is fast enough.

This chapter explores response time research related to the Web, and features an interview with Dr. Ben Shneiderman, noted HCI researcher.

Figures

  • Figure 1.1 - Shackel's Acceptability Paradigm
  • Figure 1.2 - Web site structure: From information to experience design
  • Figure 1.3 - Latency quality ratings show a drop-off at around 8 to 10 seconds
  • Figure 1.4 - The non-linear Windows file copy animation

Summary

  • Load in under 8.6 seconds (non-incremental display).
  • Decrease these load times by 0.5 to 1.5 seconds for dynamic transactions.
  • Minimize the number of steps needed to accomplish tasks to avoid cumulative frustration from exceeding user time budgets.
  • Load in under 20 to 30 seconds (incremental display) with useful content within 2 seconds.
  • Provide performance information and linear feedback.
  • Equalize page download times to minimize delay variability.

Further Reading

Books

Affective Computing
by Rosalind Picard (Cambridge, MA: MIT Press, 2000). Computers can respond supportively to reduce delay-induced frustration.
Designing the User Interface: Strategies for Effective Human-Computer Interaction, 3d ed.
by Ben Shneiderman (Reading, MA: Addison-Wesley, 1998). An excellent HCI book for designers.
Designing Web Usability
by Jakob Neilson (New Riders Publishing, 2000). "...fast response times are the most important design criterion for web pages."
E-Commerce User Experience
by Jakob Nielsen, Rolf Molich, Carolyn Snyder, and Susan Farrell (Fremont, CA: Nielsen Norman Group, 2001). This invaluable book revealed the mythical 207 usability design guidelines.
Engineering Psychology and Human Performance, 3d ed.
by Christopher D. Wickens and Justin G. Hollands (Upper Saddle River, NJ: Prentice Hall, 1999). A classic HCI text.
Human Factors and Web Development, 2d ed.
Julie Ratner ed. (Mahwah, NJ: Lawrence Erlbaum Associates, 2002). This book gathers the latest web-related HCI research into once concise volume.
Persuasive Technology: Using Computers to Change What We Think and Do
by B. J. Fogg (San Francisco: Morgan Kaufmann, 2002). Nine years in the making, Fogg's book reveals how web sites, software, and mobile technology can change people's minds and persuade them to take action. Includes a chapter on the factors that influence credibility on the web (including slow response times) with results and design guidelines from his 1998 and 2002 web credibility surveys. See also WebCredibility.org.
Self-Efficacy: The Exercise of Control
Albert Bandura (New York: W. H. Freeman, 1997). As we grow more confident with experience, we believe we can accomplish more with a desired level of performance.
The Trouble with Computers: Usefulness, Usability, and Productivity
by Thomas K. Landauer (Cambridge, MA: MIT Press, 1995). "...sadly, most reengineering efforts fail." A sobering book on computers and productivity.

Article Highlights

A Model of Web Site Browsing Behavior Estimated on Clickstream Data (PDF, 828K)
Randolph E. Bucklin and Catarina Sismeiro (Los Angeles, CA: UCLA, 2001). Clickstream-based analysis suggests that visitors trade off the number of pages requested and the time spent at each page.
Designing for Delay in Interactive Information Retrieval
Chris Roast, Interacting with Computers 10 (1998): 87-104. Introduced the notion of attunability. Consistency in response rates is important for user satisfaction.
The Economic Impacts of Unacceptable Web-Site Download Speeds
Zona Research, Zona Market Bulletin (Redwood City, CA: Zona Research, 1999). The oft-quoted "Need for Speed I."
GVU's Tenth World Wide Web User Survey
by Colleen Kehoe et al. (1999). Over half of those surveyed cited slow downloads as a problem.
How Tolerable Is Delay? Consumers' Evaluations of Internet Web Sites after Waiting
Benedict G. C. Dellaert and Barbara E. Kahn, Journal of Interactive Marketing 13, no. 1 (1999): 41-54. Found that countdown feedback nearly negates the negative effects of waiting for the web for retrospective evaluations.
Improving Web Site Design
Melody Y. Ivory and Marti A. Hearst, IEEE Internet Computing, Special Issue on Usability and the World Wide Web 6, no. 2 (2002): 56-63.
The Need for Speed II (PDF, 132K)
Zona Research, (Redwood City, CA: Zona Research, 2001). Found that although B2B sites have doubled their speed, consumer sites have become 20 percent slower.
Optimizing Page Load Time
Google engineer Aaron Hopkins tests of reducing latency for multiple HTTP requests reveal that turning on keep-alive and spreading the requests over four domains (for more than 12 objects per page) can significantly reduce latency (by 1/4).
Quality is in the Eye of the Beholder: Meeting Users' Requirements for Internet Quality of Service
Anna Bouch, Allan Kuchinsky, and Nina Bhatti, in Proceedings of CHI2000 Conference on Human Factors in Computing Systems (New York: ACM Press, 2000), 297-304.
Quantifying the Relationship between Website Download Time and Abandonment by Users
In a test of 63 respondents, Simon Galbraith and Neil Davidson found page load times between 6 and 15 seconds had high bailout rates and caused significant frustration among users. "Any wait beyond that is highly likely to cause the user to abandon the site." Red Gate Software.
Response Time and Display Rate in Human Performance with Computers
Ben Shneiderman, Computing Surveys 16, no. 3 (1984): 265-285. Keep it under 1 to 2 seconds, please.
The effect of network delay and media on user perceptions of web resources
Julie A. Jacko, Andrew Sears, and Michael S. Borella, Behaviour & Information Technology 19, no. 6 (2000): 427-439.
System Response Time and User Satisfaction: An Experimental Study of Browser-based Applications
in Proceedings of the Association of Information Systems Americas Conference (2000). John Hoxmeier and Chris DiCesare found that user satisfaction is inversely related to response time. They said that response time "could be the single most important variable when it comes to user satisfaction."
The Top Ten New Mistakes of Web Design
Jakob Nielsen found that 84% of twenty prominent sites had slow download times.
This Computer Responds to User Frustration: Theory, Design, and Results
Jonathan Klein, Youngme Moon, and Rosalind W. Picard, Interacting with Computers 14, no. 2 (2002): 119-140.
WebQual: A Web Site Quality Instrument
Eleanor T. Loiacono, Richard T. Watson, and Dale L. Goodhue, American Marketing Association: Winter Marketing Educators' Conference 13 (Austin, Texas: American Marketing Association, 2002): 432-438. A 12-factor web quality super-model from a user's perspective.
Worth the Wait
Peter Bickford, Netscape's Developer Edge (Mountain View, CA: Netscape Communications, 1997). Found that feedback increased user attention thresholds. (page offline, Wayback Machine URL listed)

General HCI and Performance Resources

Empirix
Performance evaluation tools and services.
Gomez, Inc.
Web site performance measurement and monitoring for larger clients.
HCI Bibliography
Offers human-computer interaction resources, by Gary Perlman.
Keynote Systems
Offers web site performance measurement and research.
Mercury Interactive
Offers web site performance measurement products and services.
Useit.com
Jakob Nielsen's usability portal includes his biweekly newsletter, Alertbox.
Web Criteria (now Core Metrics)
Offers automated usability tools (Site Analyst) that can find e-commerce bottlenecks to increase conversion rates.
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Last modified: January 11, 2010.

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