Model based design keystroke level model

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 1988) 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”

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

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?)

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

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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 = 4.4 + 0.20n sec

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

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