CHAPTER 2: Guidelines, Principles, and Theories Designing the User Interface: Strategies for Effective Human-Computer Interaction Fifth Edition Ben Shneiderman & Catherine Plaisant in collaboration with Maxine S. Cohen and Steven M. Jacobs

Two dimensions to design rules authority and generality Standards – specific design rules high authority and limited in application Guidelines - low in authority and general

Principles – abstract design rules high generality and low authority More fundamental, widely applicable, and enduring than guidelines Theories Beyond the specifics of guidelines Principles are used to develop theories

Standards Usually set by national & international bodies ISO Standard 9241 Example

Guidelines Shared language Best practices Critics Proponents Too specific, incomplete, hard to apply, and sometimes wrong Proponents Encapsulate experience

Navigating the interface Sample of National Cancer Institute’s guidelines: Standardize task sequences Use thumbnails to preview large images Ensure that embedded links are descriptive Use unique and descriptive headings Use check boxes for binary choices

Organizing the display Smith and Mosier (1986) offer five high-level goals Consistency of data display Efficient information assimilation by the user Minimal memory load on the user Compatibility of data display with data entry Flexibility for user control of data display

Principles More fundamental, widely applicable, and enduring than guidelines Need more clarification/interpretation Fundamental principles Determine user’s skill levels Identify the tasks Five primary interaction styles Eight golden rules of interface design Prevent errors Automation and human control

Determine user’s skill levels “Know thy user” Design goals based on skill level Novice or first-time users Knowledgeable intermittent users Expert frequent users Multi-layer designs

Identify the tasks Task Analysis usually involve long hours observing and interviewing users Decomposition of high level tasks Relative task frequencies

Interaction styles Direct Manipulation Menu selection Form fill-in Command language Natural language

Golden Rules (Heuristics) Broad-brush design rules, may not be applicable in every case Shneiderman’s Golden Rules of Interface Design convenient and succinct used in design, but can be used in evaluation relate to abstract principles

Schneiderman’s 8 golden rules of interface design Strive for consistency Cater to universal usability Offer informative feedback Design dialogs to yield closure Prevent errors Permit easy reversal of actions Support internal locus of control Reduce short term memory load

Theories Beyond the specifics of guidelines Principles are used to develop reliable, broadly useful theories Theories – descriptive, explanatory prescriptive or predictive Theories concern: motor, perceptual, or cognitive skills

More on theories Descriptive theories provide consistent terminology Explanatory theories: Observing behavior Describing sequence of activities Conceiving of designs Comparing high-level concepts of designs Prescriptive theories: Giving designers clear guidance for choices Predictive theories: Enable designers to compare proposed designs for execution time or error rates

Perceptual, Cognitive, & Motor Skills Perceptual or Cognitive subtasks theories Predicting reading times for free text, lists, or formatted displays Motor-task performance times theories: Predicting keystroking or pointing times

Consistency An important goal for designers is a consistent user interface. Consistency for objects and actions/commands Consistent use of color, layout, icons fonts, button sizes etc. If terminology for objects and actions is orderly and describable by few rules, users will be able to learn and retain them easily.