This document provides an introduction to GOMS (Goals, Operators, Methods, and Selection rules), a usability analysis technique for quantitatively comparing the efficiency of different interface designs. It explains that GOMS involves defining a task, breaking it down into basic gestures like keystrokes and mouse clicks, applying mental operators, and adding up the time estimates for each step. An example compares the time taken to enter a date of birth on Facebook, Yahoo, and a single text field, finding the single field takes around half the time of the other options. The document encourages using GOMS alongside other qualitative usability tools and provides resources for learning more about the technique.

1. GOMS analysis
On the back of the envelope

2. GOMS
Is not a venereal disease...

3. GOMS
It is a simple technique for quantitatively
comparing the efficiency of designs
BTW… when I say GOMS I mean
GOMS keystroke level Model
(KLM or KLM-GOMS)
Use it in conjunction with your
qualitative tools

4. You'll need the following tools
+ + +

5. A quick story...
Deutsche Bank Trading Floor
London 2011

7. Numbers are compelling

8. When to use GOMS
There are 3 reasons you might want to use
GOMS analysis:
1. Speed matters
2. You need to convince stakeholders
3. You want to become a better designer

9. The premise
The time taken to perform a task is the sum of
the time it takes to perform the elementary
gestures that make up that task

10. The steps
1. Define the task
2. Break it down into its gestures
3. Apply mental operators
4. Add up the numbers

11. 1. Define the task
KLM models the interaction of an experienced
user doing a defined task.

12. 2. Break it down into its gestures
KLM has a basic set of gestures; each with a
typical time assigned to it - which is sufficient
for comparative analyses.

13. 2. Break it down into its gestures
Keying (K)
= 0.2 sec

14. 2. Break it down into its gestures
Pointing (P)
= 1.1 sec

15. 2. Break it down into its gestures
Homing (H)
= 0.4 sec

16. 2. Break it down into its gestures
Mentally preparing (M)
= 1.35 sec

17. 2. Break it down into its gestures
Responding (R)
= n sec

18. 3. Apply mental operators
The hardest part of KLM. But it all comes down
to chunking.
Gestures
Chunk Chunk Chunk
M + Chunk M + Chunk M + Chunk

19. 3. Apply mental operators
M + HPK
Helen of Troy: M + KKKKKKKKKKKKKKK
356.34: M + KKKKKK
KLM: M+ K M+ K M+ K

20. 4. Add up the numbers
HMPK
0.4 + 1.35 + 1.1 + 0.2
= 3.05 sec

21. Example: Date of birth
What's your pet way of collecting date of birth?
Facebook:
Yahoo:
Single masked
input field:

22. Facebook: 3 drop-downs
Click on month, select 'July'
MPK MPK
Click day, select '11'
MPK MPK
Click year, scroll, wait, mouse off
MPK MP R MP (where R=1.0)
Select '1980'
MPK
21 sec

23. Yahoo: Input, drop-down, input
Click day, type '11'
MPK HMKK
Click month, select 'July'
HMPK MPK
Click year, type '1980'
MPK HMKKKK
15.7 sec

24. Single masked input field
Click field, type '11'
MPK HMKK
Type '07'
MKK
Type '1980'
MKKKK
8.7 sec

25. Date of birth results
Single masked input field ~2.5 times faster!
21 sec
15.7 sec
8.7 sec

26. Happy GOMSing
You now know enough to start using KLM-
GOMS on your projects!
For more guidance I recommend Jef Raskin’s
“The Humane Interface”

27. Thanks!
@AndrewUX
designthinkage.com