(based on Shneiderman chapter 11)

If one is sacrificed to the other, most users will reduce or discontinue use of the system.

User perception of the system is important

Presentation styles are developed with the balance in mind

Several dimensions of presentation style are discussed

• Use of color
• Display layout and design
• Error message design
• Nonanthropomorphic design

• Draw user attention (e.g. to warning)
• Distinguish between items
• Emphasize item groupings
• Evoke emotion in user
• Make the display more attractive (relative to audience)

Here are a few color guidelines from Shneiderman (p. 398-402)

Design in black and white. Layout, not color, should be first consideration. Use white space or lines to group and separate groups. Consider highlighting text in bold or italics.

Use color to differentiate items in dense layout. Or to allow greater density. Balance with desire to design in monochrome.

Color scheme should support task. If task OA have associated colors, corresponding interface OA should have same colors.

Be aware of traditional/cultural meanings associated with colors. Balance with coloring to support task.

Use dynamic color changes to support dynamic status changes. Depends on task, but will draw user attention to the status change.

Color scheme should be applied consistently. Otherwise, information may be misinterpreted (e.g. nonrelated items encoded in same color may be mistakenly grouped by user).

Consider user eyesight deficiencies. Consider colorblind users, and avoid color pairings that are incompatible in anyone's vision (too close or too far apart on color spectrum -- red and blue are far apart; it is difficult to focus on both at once).

Allow user control over coloring. Provide alternative schemes with easy selection mechanism.

There are benefits to performance and error rates:

• Both can be improved dramatically through effective display design.
• One form fillin system from Bell telephone saved 3.3 seconds per form by switching from narrative to structured display. Total savings over system life were nearly 80 person-years!
• Density seems to affect performance rates more than error rates.

Effective display design requires combination of:

• Task knowledge
• Graphic design,
• Principles of perception,
• and more

Most important overall guideline: design primarily for task, secondarily for real estate.

• Provide all necessary data in correct sequence
• Organize related items into groups
• Consistent and orderly formatting (such as placement and justification)

Style should be: (in alphabetical order)

• appropriate
• cohesive
• comprehensive
• consistent
• distinct
• elegant

Different displays for different types of user, even with same system, may be most effective. (e.g. expert users deal with information-dense displays much better than novices)

Some common guidelines for display design:

• Consistency is essential for multi-display systems: format, terminology, location
• Context is important for multi-display sequences, so user has idea of how far along he/she is
• Organize related items into visually separate groups
• Place items and groups on display in simple visual manner (columns, justification)
• Information density should be appropriate to task and user
• Data needed for user to make decision should be visible on display
• Many others too numerous to list (e.g., Shneiderman p 386).

It is possible to define and measure layout metrics.

Tullis study develops 4 task-independent metrics for character displays:

• overall density,
• local density (around each character,),
• grouping (e.g. size of character groups),
• layout complexity.

Example of a task-dependent metric: layout appropriateness

• How well users can follow linear sequence through UI to task completion.
• Lots of jumping around while specifying input, wastes time.
• This includes distances traversed by mouse.

Error Messages

Last reviewed: 23 November 1998