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7. Support internal locus of control. Experienced users strongly desire the sense
that they are in charge of the interface and that the interface responds to
their actions. They don't want surprises or changes in familiar behavior, and
they are annoyed by tedious data-entry sequences, difficulty in obtaining
necessary information, and inability to produce their desired result.
8. Reduce short-term memory load. Humans' limited capacity for information
processing in short-term memory (the rule of thumb is that we can remember
"seven plus or minus two chunks" of information) requires that designers
avoid interfaces in which users must remember information from one screen
and then use that information on another screen. It means that cell phones
should not require re-entry of phone numbers, web-site locations should
remain visible, multiple-page displays should be consolidated, and sufficient
training time should be allotted for complex sequences of actions.
These underlying principles must be interpreted, refined, and extended for
each environment. They have their limitations, but they provide a good starting
point for mobile, desktop, and web designers. The principles presented in the
ensuing sections focus on increasing users' productivity by providing simplified
data-entry procedures, comprehensible displays, and rapid informative feed-
back to increase feelings of competence, mastery, and control over the system.
2.3.5 Prevent errors
66 There is no medicine against death, and against error no rule has
been found.
1.99
Sigmund Freud
(inscription he wrote on his portrait)
The importance of error prevention (the fifth golden rule) is so strong that it
deserves its own section. Users of cell phones, e-mail, spreadsheets, air-traffic
control systems, and other interactive systems make mistakes far more fre-
quently than might be expected. Experienced analysts make errors in almost
half their spreadsheets, even when the spreadsheets are used in making impor-
tant business decisions (Panko, 2008).
One way to reduce the loss in productivity due to errors is to improve the
error messages nrovided by the interface Better error messages can raise
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70
Chapter 2 Guidelines, Principles, and Theories
2.3.4 The Eight Golden Rules of interface design
This section focuses attention on eight principles, called “Golden Rules,” that are
applicable in most interactive systems. These principles, derived from experience
and refined over three decades, require validation and tuning for specific design
domains. No list such as this can be complete, but it has been well received as a
useful guide to students and designers. The Eight Golden Rules are:
1. Strive for consistency. Consistent sequences of actions should be required in
similar situations; identical terminology should be used in prompts, menus,
and help screens; and consistent color, layout, capitalization, fonts, and so
on should be employed throughout. Exceptions, such as required confirma-
tion of the delete command or no echoing of passwords, should be compre-
hensible and limited in number.
2. Cater to universal usability. Recognize the needs of diverse users and design for
plasticity, facilitating transformation of content. Novice to expert differences,
age ranges, disabilities, and technological diversity each enrich the spectrum
of requirements that guides design. Adding features for novices, such as
explanations, and features for experts, such as shortcuts and faster pacing, can
enrich the interface design and improve perceived system quality.
3. Offer informative feedback. For every user action, there should be system feed-
back. For frequent and minor actions, the response can be modest, whereas
for infrequent and major actions, the response should be more substantial.
Visual presentation of the objects of interest provides a convenient environ-
ment for showing changes explicitly (see the discussion of direct manipula-
tion in Chapter 5).
4. Design dialogs to yield closure. Sequences of actions should be organized into
groups with a beginning, middle, and end. Informative feedback at the com-
pletion of a group of actions gives operators the satisfaction of accomplish-
ment, a sense of relief, a signal to drop contingency plans from their minds,
and an indicator to prepare for the next group of actions. For example,
e-commerce web sites move users from selecting products to the checkout,
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4. Design dialogs to yield closure. Sequences of actions should be organized into
groups with a beginning, middle, and end. Informative feedback at the com-
pletion of a group of actions gives operators the satisfaction of accomplish-
ment, a sense of relief, a signal to drop contingency plans from their minds,
and an indicator to prepare for the next group of actions. For example,
e-commerce web sites move users from selecting products to the checkout,
ending with a clear confirmation page that completes the transaction.
5. Prevent errors. As much as possible, design the system such that users cannot
make serious errors; for example, gray out menu items that are not appro-
priate and do not allow alphabetic characters in numeric entry fields
(Section 2.3.5). If a user makes an error, the interface should detect the error
and offer simple, constructive, and specific instructions for recovery. For
example, users should not have to retype an entire name-address form if
they enter an invalid zip code, but rather should be guided to repair only
the faulty part. Erroneous actions should leave the system state unchanged,
or the interface should give instructions about restoring the state.
2.3 Principles
71
6. Permit easy reversal of actions. As much as possible, actions should be
reversible. This feature relieves anxiety, since the user knows that errors can
be undone, and encourages exploration of unfamiliar options. The units of
reversibility may be a single action, a data-entry task, or a complete group of
actions, such as entry of a name-address block.
7. Support internal locus of control. Experienced users strongly desire the sense
that they are in charge of the interface and that the interface responds to
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