Usability inspection methods

1. Usability inspection methods User-free methods A simulation of user activities performed by the designer Performed either formatively or summatively Formative=throughout design cycle Summative=at completion of the whole cycle User-engaged methods Performed at end of design cycle with prototypes or Beta versions

2. User-free methods GOMS modeling Fitt’s Law application • Cognitive walkthrough Heuristic evaluation

3. Predictive Cognitive KLM Keystroke level model GOMS Card, Moran and Newell Goals, Operators, Methods, Selection Card, Moran and Newell Modeling the User Models

4. t sec. KLM-GOMS (What Raskin refers to as GOMS) Keystroke level model 1. Predict 2. Evaluate x sec. Action 1 Action 2 y sec. Action 3 + z sec. Time using interface 1 Time using interface 2

5. Raskin excludes Symbols and values Remarks Time (s) Operator Press Key Mouse Button Press Point with Mouse Home hand to and from keyboard Drawing - domain dependent Mentally prepare Response from system - measure 0.2 .10/.20 1.1 0.4 - 1.35 - K B P H D M R Assumption: expert user

6. 0.2 .10/.20 1.1 0.4 - 1.35 - K B P H D M R Raskin’s rules Rule 0: Initial insertion of candidate M’s M before K M before P iff P selects command i.e. not when P points to arguments Rule 1: Deletion of anticipated M’s If an operator following an M is fully anticipated, delete that M. e.g. when you point and click

7. 0.2 .10/.20 1.1 0.4 - 1.35 - K B P H D M R Raskin’s rules Rule 2: Deletion of M’s within cognitive units If a string of MK’s belongs to a cognitive unit, delete all M’s but the first. e.g. 4564.23 Rule 3: Deletion of M’s before consecutive terminators If a K is a redundant delimiter, delete the M before it. e.g. )’

8. 0.2 .10/.20 1.1 0.4 - 1.35 - K B P H D M R Raskin’s rules Rule 4: Deletion of M’s that are terminators of commands If K is a delimiter that follows a constant string, delete the M in front of it. Rule 5: Deletion of overlapped M’s Do not count any M that overlaps an R.

9. 0.2 .10/.20 1.1 0.4 - 1.35 - K B P H D M R Example 1 Temperature Converter Choose which conversion is desired, then type the temperature and press Enter. Convert F to C. Convert C to F. Apply Rule 0 HPBHKKKKK HMPMBHMKMKMKMKMK Apply Rules 1 and 2 HMPBHMKKKKMK Convert to numbers .4+1.35+1.1+.20+.4+1.35+4(.2)+1.35+.2 =7.15

10. 0.2 .10/.20 1.1 0.4 - 1.35 - K B P H D M R Example 2

11. expertise • problem-solving • error-free • abstract and idealized Weaknesses

12. Fitts’ Law Not Fitt’s law! Models movement time for selection tasks • The movement time for a well-rehearsed selection task • increases as the distance to the target • increases • decreases as the size of the target • increases

13. Fitts’ Law Time (in msec) = a + b log2(D/S+1) where a, b = constants (empirically derived) D = distance S = size

14. Cognitive walkthrough A method of analyzing designs solutions in terms of exploratory learning A method used with new designs or walk-up-and-use systems. Assumes the user is a novice. • Because user is new, of particular interest are • User success rates • User ability to recover from errors

15. Cognitive walkthrough Designer simulates the way users explore and gain familiarity with a new interface • Start with a goal or rough plan of what you want to achieve • Explore system looking for actions to achieve goal • Choose actions whose description or appearance match anticipated goals • Interpret system response and assistance in achieving goal

16. Cognitive walkthrough-example I. Task description--Describe user task from her perspective-Example: Check spelling of paper II. Identify initial goals--State user goal structure Example: Start word processor, load paper, run spell checker III. Simulate task--walk through, reviewing actions necessary to achieve task. IV. Predict behavior--anticipate user behavior and the difficulties encountered given her goal structure.

17. Cognitive walkthrough I.Describe the user-level of experience,mental models II. Describe task form user perspective III. Make a numbered list of actions user should perform toe complete task IV. List goals user is likely to form when starting task.

18. Heuristic evaluation Analysis by a team of analysts using a variety of informal methods • Start by assembling a group of four to six evaluators • Develop a set of design heuristics to guide evaluators • Have team evaluate the design using the set

19. Design heuristics Provides simple and natural dialogue Speaks the user’s language Maintains consistency Provides feedback Minimizes memory load Provides clear marked exits Prevents errors Allows for error recovery Provides clear navigation