GOMS Timing for WIMP interfaces When (fine-grained) speed matters

2 K - keypress P - point with mouse C - click with mouse H - home hands on new device M - mentally prepare R(t) - system response time

K - keypress P - point with mouse C - click with mouse H - home hands on new device M - mentally prepare R(t) - system response time 3

4 K – keypress P - point with mouse (Fitt's Law)‏ C - click with mouse.2 H - home hands on new device.4 M - mentally prepare 1.35 R(t) - system response time ?

5 NOTES: M before K/C or P except MPMC... becomes just … MPC because C “anticipated” –e.g. move mouse to target and click MKMKMK... MKKK for cognitive unit –e.g. type “cat”

6 Method 1 – highlighting “the cat” Assumptions: hands were on keyboard R = 0 Experienced typist H Reach for mouse M – 1.35 – mentally prepare P Point to the left of "the" C – Click mouse down and hold M – 1.35 – mentally prepare P Point to right of "cat" C Release mouse Total = 5.7

About K, P, R  You need to consider each of these  What assumptions can you make?  Record them  Then select the value(s) that are reasonable  You may need to creates branches which assess different values

8 Method 1 cont – bolden keyboard shortcut M – 1.35 – mentally prepare K Press and hold "Control" K Press "B" K Release "Control" Total = 3.15

9 Method 2 - use menu Assumptions: as before  M – 1.35 – mentally prepare P Point to "Format" menu C – Click and hold M – 1.35 – mentally prepare P Point to "Bold" menu item C – Release mouse Total = 5.40

10 Conclusion for this case Assumptions: Hand position, R, K, P Common part is 5.7 (sweeping out “the cat”)‏ Rest: –Keyboard shortcut takes 3.15 seconds –Mouse menu method takes 5.4 seconds

11 Other cases to consider? Consider each assumption: Hand position, R, K, P Other representative tasks

12 Summary of approach Focus on speed Known sequence of operations Can predict performance for experienced users Walkthrough steps, calculate time for each step, sum Can sometimes predict choices of method

13 Summary of uses Relatively inexpensive Can be used to compare “methods” Challenging to apply for conventional interfaces.... pervasive? Expert users only Would you expect software that assist in this?

14 Postconditions (exam questions) Critique the relevance of GOMS in a particular context: user expertise, timing in project, usability targets, available expertise of evaluators Compare and contrast with other UE methods Application of keystroke analysis for a given task Application timing analysis, with particular care about assumptions Critique a keystroke or timing analysis: strengths and limitations

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