Evaluation TypesGOMS and KLM

CS352

Announcements

• Mid-term Tue of Week 5• Project presentations

– Your users (before mid-term)• Next milestone of you project will be out later

today or tomorrow (Prototypes)• Reading

– 12.3 (evaluation methods), 15.4 (GOMS)

2

Where we are in PRICPS:

• Predispositions: Did this in Project Proposal.

• RI: Research was studying users. Hopefully led to Insights.

• CP: Concept and initial (very low-fi) Prototypes due some time next week

• Evaluate throughout, repeat iteratively!!

Evaluation

• Analytical – based on your head• Empirical – based on data

– Formative • inFORMs design• what is (still) needed?

– Summative • did it work?

Analytical methods

• You follow established guidelines/procedures/models to decide (in your head) how good your design is.

• Examples:– GOMS/KLM – for skilled users, no errors.

• evaluating efficiency of regular use.

– Heuristic Evaluation– Cognitive Walkthrough – for first-time users.

• evaluating ease of learning.

GOMS (and KLM)

• GOMS: a family of models.• Predict user performance.• Useful for predicting actual time a user will

take in UI.• Useful for comparing different UIs.

GOMS Constructs

• Goal, Operators, Methods, Selection rules• Goal: “what”. • Method: “how” steps (learned).• Operators: Cognitive processes + physical

actions to DO it.• Selection rules: rules saying which method

to select.

GOMS example:Delete a word

• Goal: delete a word in a sentence.• Method #1: use the menu

– Recall that the word has to be highlighted.– Recall that the command is “cut”.– Recall that “cut” is in the Edit Menu.– Accomplish goal of selecting and executing

“cut”.– Return: goal accomplished.

GOMS example (cont.)

• Method #2: use the delete key– Recall where to position cursor in relation to

word to be deleted.– Recall which key is delete key.– Press “delete” key to delete each letter.– Return: goal accomplished.

• Operators used in these methods– Click mouse, Drag cursor over text, Select

menu, Move cursor, Press KB key, Recall, ...

GOMS example (cont.)

• Selection rules:– Use mouse/menu method (#1) if there’s a lot

of text to delete.– Else use “delete” key (method #2).

Applications of GOMS

• Various application and fields– Telephone operator workstation using CPM-

GOMS – CAD system for ergonomic design using

NGOMSL – Intelligent tutoring system using NGOMSL– Mouse driven text editor using KLM – Bank deposit reconciliation system using KLM– Space operations database system using

KLM

Telephone operator workstation using CPM-GOMS

• The task: a telephone company operator responding to customer requests for assistance.

Limitations of GOMS [Card et al. (1980) ]

• applied to skilled users, not to beginners or intermediates.

• doesn't account for either learning of the system or its recall after a period of disuse.

• doesn't account for errors. • does not address the amount and kind of fatigue• individual differences among users is not

accounted for in the model.

KLM (a low-level variant of GOMS)

• Keystroke Level Model.• Simple, but accurate. Widely used.• Scope:

– skilled users– doing a task error-free.– using a specific method in a UI.

• CogTool has this built-in.

KLM Operators

• User Operators:– K (keystroke), P (point), H (homing), D

(drawing), M (mental: think).– Times for each are provided to you

• based on extensive research/empirical data.

• System Operator:– R (respond).

KLM/GOMS example 1:Open a file

• 27 ways to open a file in Windows!

• Methods as states +transitions.

• (High opgranularitycombineslow-level ops.)

KLM/GOMS example 1 (cont.)

• Used to:– Understand cost

of each. – (break down

participants actual costs).

– “RL”:recent lists.– “WS/WX”:search.

• And to...

KLM/GOMS example 1 (cont.)

• Use the breakdowns to compare costs to new UI alternative (new feature “FP”)

actual calc’d

Hick’s Law

• GOMS’s “S” stands for “Selection”• Hick’s Law predicts the time to make a choice

between multiple choices, n is the # of choices:

Fitts’ Law

• Predicts that the time required to rapidly move to a target area is a function of the distance to and the size of the target

In practice…

• GOMS not used often• Fitts’ law often used for determining best

case for new kinds of input methods

CogTool Example

• CogTool examples.– Calculating the cost of the task in this UI.– Comparing the cost if do the task with

different widgets.– Where are these cost differences coming

from?• under the hood to ACT/R

What’s coming up next:

• Heuristic Evaluation• Cognitive Walkthroughs• Empirical Studies