|
|
UI Design Update
Newsletter – August, 2003
Insights from
Human Factors International
|
Are We There Yet? Effects of Delay on User Perceptions of Web Sites
|
| |
|
|
|
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.
|
| |
| The
Pragmatic Ergonomist |
| |
|
|
| |
|
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.
|
|
Putting
Research into Practice seminar
Suggestions, comments,
questions?
HFI editors at
|
