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Top 5 Usability Principles


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A presentation that defines usability, the nature of users, and 5 high-level principles for guiding your software design.

Top 5 Usability Principles

  1. 1. Top 5: Usability Principles Erik Ralston BIS BoF April 15, 2010 1
  2. 2. What is Usability? A subjective evaluation of how easily users achieve goals Minimize user error and maximize user satisfaction Learning in the short-term and efficiency in the long-term 2
  3. 3. What is Usability? Communicated by user’s emotional response Users either “love” or “hate” the application “Mental Model” – A User’s internal understanding and expectations on how the system works Often very different than the real system internals “Intuitive” – Resonant with a user’s mental model Easy to Learn Familiar to Users 3
  4. 4. Understanding the User “Intuition” is built from emotionally rooted expectations and beliefs (biases resulting from previous experiences) Intuition is considered before reason Everyone's intuition is different; you must ask the user! Humans with neurologically hindered emotions often suffer from indecision and lack of motivation (Aboulia) Not evoking emotion makes the user unmotivated 4
  5. 5. Understanding the User Spock uses only Vulcan logic 5
  6. 6. Understanding the User Stephen uses only his gut 6
  7. 7. Understanding Errors “Slip” – A temporary malfunction of the user Typing an extra letter Missing a click “Mistake” – A mismatch between user’s mental model and the real behavior of the system Gulf of Execution Gulf of Evaluation More a continuum than absolute categories Misspelling a word can be caused by either 7
  8. 8. Understanding Errors 8
  9. 9. Gulf of Execution “I don’t know what to do???” User can’t connect their goal to a decision in the interface Users are unaware of a decision that affects their goal 9
  10. 10. Gulf of Evaluation “What does that mean???” “What did I just do???”, “Where am I???” User can’t match current state to mental model User can’t connect a previous decision with a new state User was unaware they just made a decision that changed state The user just feels… 10
  11. 11. Gulf of Evaluation 11
  12. 12. What is an interface really? An abstraction of the system for user interaction Enables user to act on the system Provides feedback from the system to the user A purposeful barrier between the user and the system Protects user from complexity Obfuscates even simple aspects of system 12
  13. 13. What is an interface really? Decisions – Actions the user may perform on the system Information – System data relevant to user Instructions – Description of decisions or information 13
  14. 14. What is an interface really? 14
  15. 15. What is an interface really? 15
  16. 16. Engineering “Intuitive” Suggestions for connecting interface to mental models Managing presentation of information, decisions, and instructions NOT infallible laws or requirements Embody the fundamentals of all good design Simplicity Consistency Clarity Principles extend to some everyday items as well 16
  17. 17. #5: Progressive Disclosure Maintain user focus by initially showing simple and relevant items; hiding advanced and rarely used items. 17
  18. 18. Recognition 18
  19. 19. Recognition 19
  20. 20. Recognition 20
  21. 21. Recognition 21
  22. 22. Progressive Disclosure 22
  23. 23. Progressive Disclosure Show the most common items and hide the rest 20% of the interface provides 80% of the functionality Users can only read in a small radius; think 1 inch If an item is uncommon or very complicated, hide it Show users “their” information first (personalization) If a task is recent, then show it first 23
  24. 24. #4: No Dead Ends (or Death Traps) At no time should a conspicuously valid decision lead to obstruction of the user goal, or even worse harm 24
  25. 25. No Dead Ends 25
  26. 26. No Dead Ends 26
  27. 27. No Dead Ends 27
  28. 28. No Dead Ends 28
  29. 29. No Dead Ends In Detail If a user decision would cause a system error or invalid state, then that decision should be inaccessible Hidden or disabled If a user decision is ambiguous, then accept ambiguity Error messages should guide the users on how to re- establish a path to their goals 29
  30. 30. #3: Recognition Over Recall Economize user memory by offering options instead of forcing recall of previous information 30
  31. 31. Recognition Over Recall Miller’s Law – Working memory is 7± 2 Items 31
  32. 32. Recognition Over Recall In Detail If the user must remember something to make a decision, then provide them options to choose amongst Essay or multiple choice? If it’s a small idea, connect it to a large idea (Hierarchy!) If it’s the same idea, give it the same name everywhere 32
  33. 33. #2: Fitt’s Law Ease of reaching a goal is a function of size and distance 33
  34. 34. Fitt’s Law 34
  35. 35. Fitt’s Law in Detail Size implies importance If it’s used often, it should be big Proximity implies relationships If two elements are related, they should be close together If two elements are unrelated, they should be far apart Related elements elements should be adjacent Order implies path Think about a visual and logical “path” for the user to follow If a user must make a series of decisions, then they must be in a predictable order (ex: left-to-right or top-to-bottom) 35
  36. 36. #1: Affordance The possible actions for an object should be presented obviously and consistently 36
  37. 37. Affordance Very Non-Standard Buttons Interaction that is really distraction Buttons that hide their destination 37
  38. 38. Affordance In Detail Different combinations between possibility and reality “Perceptible” visible and implemented decisions “Hidden” invisible and implemented decisions “False” visible and unimplemented decisions Do not require interaction to understand the possibilities Hovering shouldn’t be necessary, but perhaps clarifying If it looks the same, it should behave the same If it looks different, it should behave differently 38
  39. 39. Top 5 Usability Principles #5: Progressive Disclosure – 80-20 Rule for Interfaces #4: No Dead Ends – Remove invalid decisions #3: Recognition Over Recall – Choice not memory #2: Fitt’s Law – Ease of use is distance and size #1: Affordance – Action possibilities 39
  40. 40. #0: Ask the User! None of the principles are more useful than user opinion Usability is about making the user happy Only the user can decide when they are happy You can’t make them happy if you don’t ask them Use the principles to guide the user They can’t understand code, but they understand Usability Use the principles to take the lead and most users will follow 40
  41. 41. Your Principles? 41
  42. 42. Other Places of Insight The guide to making government website “usable & useful” OK/Cancel A blog/web-comic on usability design Windows User Experience Interaction Guidelines Microsoft’s wisdom on User Experience 42
  43. 43. Questions? 43
  44. 44. Thank You! 44