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Errors&HelpAn ounce of prevention...
CS / Psych 6750
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Microsofts Spectacular Errors
Adobe UI GripesFall 2006PSYCH / CS 6750*
CS / Psych 6750
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AgendaError typesSlip typesError prevention guidelinesError
recovery guidelinesFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Slips versus MistakesRecall:Human errors can be classified into
slips and mistakesCan understand using Normans gulf of
executionSLIP: If you understand a system well you may know exactly
what to do to satisfy your goals: youve formulated the correct
action. But you may fail to execute that action correctly
(mis-type, press the wrong button)MISTAKE: If you dont know the
system well you may not even formulate the right goal. (Example:
you may pick the magnifying glass icon thinking it is the find
function, when it actually zooms the text).Both may be corrected
for, and designed around.
Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Errors in User-Computer DialogThree phasesRead-scan phase --
Perceptual errorsThink phase -- Cognitive errorsRespond phase --
Motor errors
Can generally lead to either slips or mistakesFall 2006PSYCH /
CS 6750*
CS / Psych 6750
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Perceptual ErrorsResult from poor perceptual cuesDisplay of
objects that are visually similarInvisible or poorly expressed
statesFailure to capture users attentionLack of perceivable
feedbackFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Perceptual ErrorsFall 2006PSYCH / CS 6750*Are perceptual errors
likely here?Tallly Ho Uniforms
CS / Psych 6750
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Cognitive ErrorsCaused by taxing memory and thinkingTax recall
memoryPoor mnemonic aidsInconsistencyLack of context or status
infoe.g., where came from in a menuMental calculations and
translationsFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Cognitive ErrorsFall 2006PSYCH / CS 6750*Are cognitive errors
likely here?
CS / Psych 6750
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Motor ErrorsTaxing the motor skillsAwkward movementsHighly
similar motor sequencese.g., double click, clickPressure for
speedRequire a high degree of hand-eye coordinationRequiring
special types of motor skills (type)Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Motor ErrorsFall 2006PSYCH / CS 6750*Lots of errors are likely
here!!
CS / Psych 6750
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Example Studies170 experienced UNIX users over 9 daysIndividual
commands error rates of 3-50%
300 security system users over 20 months12,117 error
messagesMost common 11 errors -> 65%2517 involved repeated
errors (with no non-errors in between) within 10 minutes Bad error
recovery/helpFall 2006PSYCH / CS 6750*Kraut et al, CHI 83Mosteller
& Ballas, Human Factors 89
CS / Psych 6750
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SlipsAutomatic (subconscious) error that occurs without
deliberation
Examples?Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Types of Slips1. Capture errorContinue frequently done activity
instead of intended oneType animation instead of animateConfirm
deletion of file instead of cancel2. Description errorIntended
action has much in common with others possible (usually when
distracted, close proximity)ctrl key & caps lock key / Sun
& MacFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Types of Slips3. Data driven errorTriggered by arrival of
sensory info which intrudes into normal actionCall to give someone
a number, dial that number instead4. Associative activationInternal
thoughts and associations trigger actionPhone rings, yell come
in
Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Types of Slips5. Loss of activationForgetting goal in middle of
sequence of actionsStart going into room, then forget why youre
going there6. Mode errorsDo action in one mode thinking youre in
anotherDelete file, but youre in wrong directoryFall 2006PSYCH / CS
6750*
CS / Psych 6750
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Error-handling StrategiesAvoid and prevent
Identify and understand
Handle and recoverFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Preventing ErrorsRules of thumb:Preventing slips can be done by
analysing users interaction with the application, then tweaking
screen design, button spacing, etc.Preventing many mistakes
requires that users understand the system better; may require more
radical redesign, or perhaps a totally different metaphorFall
2006PSYCH / CS 6750*
CS / Psych 6750
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Error Prevention GuidelinesEliminate modes or provide visible
cues for modesUse good coding techniques (color, style)Maximize
recognition, minimize recallDesign non-similar motor sequences or
commandsMinimize need for typingFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Error Prevention GuidelinesTest and monitor for errors and
engineer them outAllow reconsideration of action by user (e.g.,
removing file from trash)Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Error Prevention GuidelinesProvide appropriate type of
feedbackGag - Prevent user from continuingErroneous loginFall
2006PSYCH / CS 6750*
CS / Psych 6750
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Error preventionWarn user an unusual situation is occurringBell
or alert box
Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Error preventionNothing - Just dont do anything (Careful, user
must determine problem)Mac: move file to bad place
Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Error Recovery GuidelinesProvide undo functionProvide cancel
function from operations in progressRequire confirmation for
drastic, destructive commandsProvide reasonableness checks on input
dataDid you really mean to order 5000?Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Error Recovery GuidelinesHowever, before a user can recover,
must be able to detect that an error has occurredDetection:
provided by easy visibility, feedbackOther options?Self-correct -
Guess correct action & do itSpell-check correctionDialog -
System opens dialog with userGo into debugger on run-time
crashQuery - Ask user what shouldve been done, then allow error
action as legal one (did you mean?)Command language naming
errorFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Error Recovery GuidelinesReturn cursor to error field, allow
fixTell them what to fix, how to fix itProvide some
intelligenceGuess what they wanted to doProvide quick access to
context-sensitive helpFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Error Handling Example (Web)Form fill in is the most common
error caseFall 2006PSYCH / CS 6750*
CS / Psych 6750
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????Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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User Support (aka Help)Line between error recovery and help can
be fuzzy
Overarching design principle: must be as unobtrusive as
possible
Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Command AssistanceE.g., on-screen manuals, help commands (man on
Unix), etc.Simple and efficient if the user knows what he/she is
looking for and is seeking either a reminder or more detailed
informationButWhat if people dont know what theyre looking for?What
about commands that the user does not know about but needs?What
about commands the user thinks exist but do not?Command assistance
is little help here.Fall 2006PSYCH / CS 6750*
CS / Psych 6750
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Command PromptsIn CL interfaces, usage prompts are an
example.Assumes thatsystem can detect erroruser understands the
command well enough to apply the guidanceGenerally only helpful for
simple errorsFall 2006PSYCH / CS 6750*
CS / Psych 6750
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Context-sensitive HelpMove away from placing onus on user to
remember the commandOften not very sophisticatedCommon
examples:Microsofts Whats This? optionTooltipsClippy (arrrgh)Whats
the context?Just the control itself? (Simple)Users past history and
application state? (More sophisticated)Fall 2006PSYCH / CS
6750*
CS / Psych 6750
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Wizards and AssistantsAttempt to prevent errors by providing
common paths through softwareSafety, efficiency, and accuracy (as
long as its a supported task)May be unnecessarily
constrainingGuidelines: allow backward movement, show progress
indicatorAssistant: Clippy is actually an example of this. A
context-sensitive trigger to launch a wizard style interaction
Q: What went wrong with Clippy?Fall 2006PSYCH / CS 6750*
CS / Psych 6750
