An Empirical Evaluation of Undo Mechanisms

Aaron G. CassChris S.T. Fernandes

Andrew Polidore

Computer Science Dept.Union College

Schenectady, NY, USA

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Talk Outline

• Types of undo

• Problem statement

• Empirical evaluation design– Pilot study– Broad evaluation

• Results

• Future Work

• Conclusion

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Linear Undo

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Selective Undo

• Undo arbitrary action without requiring the undoing of subsequent steps [Berlage ’94]

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Selective Undo

• Script model [Archer, et al ’84]

– Removing action Ai results in state:

– A1, A2, …, Ai-1, Ai+1, …, An

• Cascading model [Cass, Fernandes ’05]

– Accounts for dependencies between actions

– If Aj dependent on existence or result of Ai

(j > i), Aj also undone

Differing semantics:

Problem Statement• Selective undo is believed to be superior

to linear undo

But…

Will it be easier for users to use?

Is this a natural model for undo?

Does it match users’ mental models?

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Goal

• Compare three different models of undo– Linear– Script selective– Cascade selective

Conduct a user study to find out!

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The Study

• Want to determine users’ mental model of undo

• Design a task that elicits their mental model in the performance of that task

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The Instrument

• Paper-based instrument– Not associated with a

computer application– User freedom– Selective undo not

widely implemented

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The InstrumentSteps taken to create this picture:

1. Draw Circle2. Draw Square3. Draw Triangle4. Color Circle

Assume you have already done the steps above. Draw what you think the outcome should be if you were to undo step 4 (step 1).

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Two Tasks

1. Draw Circle2. Draw Square3. Draw Triangle4. Color Circle

Undo Step 1

Linear ScriptCascade

Undo Step 4

All models

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Pilot Study

• Concern that word “undo” may trigger response based on past experience

• Compare with “reverse the effects of”• 4 subjects

• Result: kept “undo” in instrument wording

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Evaluation Methods

• 29 subjects– Undergraduate population– Experience with widespread applications– Little experience with specialized applications

• Within-subjects design

• Post-task questionnaire

• Single dependent variable2 analysis

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Results (N=28)

linear script cascade other

1 (4%)

7 (25%)

18 (64%)

2 (7%)

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2 Analysis

• Expected one model to be preferred

p<0.05 linear script cascade other

linear script cascade other

• Expected cascade to be preferred over linear

p<0.05

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2 Analysis• Expected script to be

preferred over linear

2 not applicable

• Expected either script or cascade to be preferred over the other

p<0.05

linear script cascade other

linear script cascade other

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Conclusions

• In familiar applications– Cascading selective is more natural than

script selective– Cascading selective is more natural than

linear– Script is more natural than linear

(the data suggests)

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Future Work

• Use a more complete application– Pilot study with presentation software already

complete

• Use a richer set of dependencies

• Implement selective undo in a representative application