UI Design Newsletter – August, 2003

Insights from Human Factors International

In This Issue:

Are We There Yet? Effects of Delay on User Perceptions of Web Sites

The Pragmatic Ergonomist

Dr. Eric Schaffer, Ph.D., CPE, founder and CEO of HFI offers practical advice.

First impressions count

Remember when your mother told you that first impressions count? Web design is finally getting to that point. Whether it is because Internet use has moved far enough across the chasm to attract more of the late adopters looking for a "user experience," or because sites have improved enough that the global frustration with poor usability no longer trumps the first impression of the site, site designers are beginning to appreciate that mom was right. First impressions count again. The shift toward emotional design reflects one of the most interesting and exciting trends in Web development so far. It will present new challenges. It will also bring old ones back into sharper focus.

One of the chronic challenges that will be highlighted by emotional design is site download speed. There are many sources of delay in Web site and application delivery. Some, such as increased Internet congestion or connection speed, are outside the control of the designer. However, other causes of delay such as page/graphic size, server-task prioritization, and incremental page presentation, are within the control of the designer and implementation team. Thus, one challenge for successful emotional designs will be creating sites that balance visually compelling and task-rich resources with quick delivery.

Speed of download is not a new problem for Web designers. Weinberg (2000) estimated that $4 billion in potential e-commerce revenue is lost each year because of download delays. But how, specifically, do delays figure into user frustration and site abandonment?

And they call this FAST food??

Actually, determining just how long someone will wait is an old problem in the service industry. Years and years of research have been dedicated to determining how waiting for service effects customers' perception of both the product and service provider. The fundamental finding of this work is reflected in Maister's First Law of Service:

Service = Perception – Expectation

In other words, customers develop positive feelings when the perceived service exceeds the expected service. With respect to delays, users are happy when the site responds as quickly, or more quickly, than they expected, and they become frustrated when the site is slower than they expected. But how long is too long to wait for a Web site?

Many groups of researchers have set out to define how delays impact users' perception of interactive sites. Not surprisingly, these studies show that users faced with long, unexplained delays during the course of interactions are dissatisfied. But how long is too long? And what is the real impact of perceived delay?

Waiting is frustrating, demoralizing, aggravating, annoying, time consuming, and incredibly expensive. — FEDEX Commercial

Study 1: Does delay impact perceived usefulness?

Sears, Jacko, and Borella (1997) created two versions of a Web site (text-only and text-plus-graphics) to examine the effects of content displayed and download delay on perceived usefulness. In this study, participants experienced delays ranging from 0.58 to 6.80 seconds and then rated sites on perceived usefulness, organization and quality of information. Users ratings reflected sensitivity to the delay for both the text-only and text-plus-graphics sites. However, ratings for text-only pages were lower than text-plus-graphics pages even at the shortest delay intervals suggesting that participants expected text-only pages to render more quickly than graphics intensive pages.

Study 2: Does delay influence how interesting a site is?

Ramsay, Barbesi, and Preece (1998) examined the effect of fixed-download delays, site type, and page style on perceived interestingness of content and ease-of-scanning. Along with delay time, they varied types of site content (scientific, business, advertisement, personal, history, instructional and entertainment) and page styles (text only, graphics with few links, balanced text and links). The delays in their experiment ranged from two seconds to two minutes. Sites with long delays were rated significantly less interesting and more difficult to scan independent of the content presented. In addition, page style did not influence the perceptions: participants expected graphics-heavy sites to respond as quickly as text sites.

Boredom results from being attentive to the passage of time itself. — William James

Study 3: Does incremental presentation shorten the delay?

Bhatti, Bouch, and Kuchinsky (2000) report a study, and related guidelines for server design, based on work exploring factors moderating Quality of Service (QoS) perceptions on e-commerce sites. For their study, Bhatti and colleagues developed an ecologically valid, yet quantifiable, task by artificially injecting download delays (ranging from 2 to 73 seconds) as participants completed a set of common tasks on a live Web site. They designed the study so that the primary task of configuring and purchasing a home computer system could be broken down into a series of subtasks by purchasing components separately. They evaluated the impact of download delay by having participants rate the tolerability of delay for each page after it had completed rendering. In a critical comparison, Bhatti and colleagues varied page presentation by having pages render either completely or incrementally. Pages rendered incrementally first displayed the page banner, followed by text and then graphics.

Consistent with previous work, Bhatti and colleagues noted that participants in the complete-rendering condition started to judge delays unacceptable at roughly 10 seconds. This is consistent with previous work in applied attention and cognition suggesting that after 10 seconds or more of wait time, the boundaries of the current 'unit task' are broken (Card, Moran, and Newell, 1983). Simply put, after 10 seconds we get bored with waiting and start to look for something else to do. As a result we lose our place in the task and sometimes even forget what we were doing.

Critically, however, Bhatti and colleagues observed a significant difference between the complete and incremental rendering conditions in their study. Participants in the incremental rendering group tolerated up to 6 times more delay. They suggest that incremental loading helps users keep their attention on the task at hand (rather than redirecting it to the task of reevaluating the Quality of Service.)

If it's a Full Professor, you wait 20 minutes. If it's an Assistant Professor, you only wait 10....

The studies outlined above converge with other findings to suggest that 10 seconds is about the edge of too long. However, this is not necessarily a hard rule. Willingness to wait is moderated by other factors. For instance, novice users and older individuals tend to be willing to wait longer for a computer to react (Schneiderman, 1998, and Selvidge, 2003, respectively). In addition, users who have little or no experience with high bandwidth connections are more patient (Selvidge, 2003). Users tend to be relatively more patient the first few times they visit a site (Bhatti, 2000). Finally, users will wait longer in the service of completing important tasks. However, these same users report higher frustration levels than counterparts who experience the same delay in completing less important tasks (Ceaparu, Lazar, Bessiere, Robinson, and Schneiderman, 2002). In this last case, willingness to wait may indicate that the user feels trapped rather than satisfied.

This brings us to Maister's Second Law of Service:

It's hard to play catch-up ball.

That is, any impression (or halo effect) created early in a service encounter will color the rest of the interaction. As such, since not all delay is under the control of the designer (e.g., user's connection speed), it is important to consider (and test!) download speeds even if you are designing for a more tolerant group. Indeed, the previously mentioned literature on perceived quality in the (physical) service sector clearly shows that the largest payback for effort and attention spent in improving the interaction occurs from improving the perception of the early stages of the interaction — reducing the waiting time (Maister, 1985).

Are we there yet?

In summary, perceived delays in site presentation undermines users' evaluation of the site. Users systematically rate slower sites as less interesting (Ramsay, Barbesi, and Preece 1998) and having lower quality content (Jacko, Sears, and Borella, 2000). In addition they report that delays interfere with task continuity, their ability to remember the site, and use flow (Shubin and Meehan, 1997). Exceedingly slow sites can lead users to believe an error has occurred (Lazar and Norico, 2000). Finally, users correlate site performance and security: Chronically slow sites are considered to be less secure resources for purchase (Bhatti, Bouch, and Kuchinsky, 2000).

In the face of increased pressure to create visually compelling designs, these findings highlight the importance of balancing performance factors with emotion.

Given the current bandwidth situation we will have to design with an eye to speed. For example:

• question the value of each graphic
• use incremental presentation
• use tricks such as preloading images for subsequent pages (at the bottom of a page, include images from subsequent pages, but size them to 1x1 pixels so they are not noticed by the user. When the user goes to the next page the images are already loaded.)
• make images lean (low bit depth, resolution, etc.)

Based on much older studies with mainframes I suspect the bar will keep moving as bandwidth improves. I therefore suspect the pressure for speed will continue past 6 seconds and level out around 2 seconds. Even faster sub-second speeds may result in a faster working pace. But 2 seconds is probably where the real target will lie.

References

Bhatti, N., Bouch, A. and Kuchinsky, Allan. (2000). Integrating User-Perceived Quality into Web Server Design. Computer Networks (33), 1-16.

Card, S. K. , Moran, T. P., and Newell, A. (1983). The Psychology of Human-Computer Interaction. Lawrence Earlbaum Associates: Hillsdale, NJ.

Ceaparu, I., Lazar, J. Bessiere, K., Robinson, J. and Schneiderman, B. (2002-Draft). Determining Causes and Severity of End-User Frustration.

Lazar, J. and Norcio, A. (2000). System and Training Design for End-User Error. In S. Clarke and Be Lehaney (Eds), Human Centered Methods in Information Systems: Current Research and Practice, 76-90. Hershey, PA: Idea Group Publishing.

Maister, D. (1985). The psychology of waiting lines. Eds. J. A. Czepiel, M. R. Solomon and C. Suprenant. Lexington Books.

Ramsay, J. Barbesi, A. and Preece, J. (1998). A psychological investigation of long retrieval times on the World Wide Web. Interacting with Computers, 10, 77-86.

Schneiderman, B. (1998). Designing the User Interface: Strategies for Effective Human Computer Interaction. (3rd Ed). Reading, MA: Addison-Wesley.

Sears, A., Jacko, J. (2000). Understanding the relation between network quality of service and the usability fob distributed multimedia documents. Human-Computer Interaction, 15(1), 43-68.

Selvidge, P. (2003). Examining Tolerance for Online Delays. Usability News 5.1.

Schubin, H. and Meehan, M. (1997). Navigation in Web applications. Interactions 4(6). 13-17.

Weinberg, B. D. (2000). Don't keep your Internet customers waiting too long at the (virtual) front door, Journal of Interactive Marketing, 14(1), 30-39.

Pat Malecek, CUA
User Experience Manager
A.G. Edwards & Sons, Inc.

+++

From The Truth About Download Time, by Christine Perfetti, User Interface Engineering:

"It seems that, when people accomplish what they set out to do on a site, they perceive that site to be fast.

If people can't find what they want on a site, they will regard the site as a waste of time (and slow). But, when users successfully complete tasks on a site, they will perceive their time there as having been well spent.

We're wondering: When users are complaining about the download speed of your site, what are they actually complaining about? Are you better off making the site load faster or ensuring that users complete their tasks?"

+++

And from Aesthetics and Usability: A Look at Color and Balance, by Laurie Brady and Christine Phillips:

"This appears to support the idea that user satisfaction is related more to successful navigation than aesthetic appearance. However, when asked to predict which of the four sites the users thought would be the easiest to use, they ranked the aesthetically pleasing site the highest."

What I like about this article is the notion that good structure *actually* helps users be successful, while good appeal helps users *feel* they will be successful (which may impact their actual success on the site and their post-use perception of the site).

Just my two cents.

Andy King

Good summary, you neglected to mention/cite my new book, "Speed Up Your Site: Web Site Optimization" which is all about this subject and cites the papers you cite (and other newer ones). The first chapter is devoted to this subject (summarizes and distills current research)

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