1. Model based design keystroke level model

2. GOMS Variants KLM - Simplest version (Card, Moran, Newell 1983)
CMN-GOMS - Original formulation; includes methods and selection rules (Card, Moran, Newell 1983)
NGOMSL - GOMS using natural language; also can model memory usage and learning times (Kieras )
CPM-GOMS - Models parallel processing by cognitive, perceptual and motor systems (John 1990)
Source: John and Kieras, “The GOMS Family of User Interface Analysis Techniques”

13. Heuristics for adding M’s
Basic idea: Put an M before each step requiring access of a “chunk” from long-term memory
Insert M’s before each K and P
K -> MK; P -> MP
Delete M’s in the middle of typing a word or string
MKMKMK -> MKKK
Delete M’s in the middle of composite actions (for example, point and click)
MPMK -> MPK
Adapted from Rob Miller

14. Limitations of KLM
Only applies to expert users doing routine (well- learned) tasks
Only predicts efficiency - not error rate, memorizability, learnability, etc.
Impractical for all but the simplest tasks
Ignores
Parallel processing
Goal interleaving
Mental workload (working memory limits, fatigue)
Planning and problem-solving (how to select a method?)

15. Model based design Card, moran and newell (CMN) GOMS

36. The End

37. Example: Deleting a Word
Using Shift-Click M
P [start of word]
B [mouse click]
P [end of word]
K [shift]
H [to keyboard]
K [Del]
Total:
3M + 2P + 2B + 2K + H
= 9.45 sec
Using Delete M
P [start of word]
B [mouse click] H
K [Del] x n [length of word]
Total: 2M + P + B+ H + nK
= n sec

38. Using KLM & CMN GOMS
KLM can help evaluate UI designs, interaction methods and trade-offs, using parametric analysis
If common tasks take too long or consist of too many statements, can provide shortcuts T
Del n times
Shift-click n
Adapted from Rob Miller

39. Example Goal: delete word (n chars long)
Select: method 1 if n > method 2 if n < 10
Method 1: Goal: highlight text & delete
Goal: highlight text
Point
Click
Shift
Verify
Method 2: Goal: delete n chars