Lecture 12: Errors - UMD Computer Science Department … · Spring 2010 CMSC 434 Introduction to...

CMSC 434 Introduction to Human Computer Interaction Spring 2010 1

Lecture 12: Errors

March 22


Medical Usability: How to Kill Patients Through Bad Design

•  Under dosage •  Double dosage •  Wrong patient •  Wrong date •  Medical history ignored •  Post-it notes


Hospital’s order-entry system

•  Misleading default values –  10 mg

•  No feedback, new commands not checked against the old ones –  Double dosage

•  Poor readability –  Wrong patient selected

•  Data description errors –  Tomorrow

•  Memory overload –  Too many screens for a patient’s medical history

•  Overly complicated overflow –  Different from Hospital's actual workflow


Lecture objectives

•  Identification –  Identify the variety of errors people make

and their possible causes

•  Prevention – Discuss guidelines to prevent the errors

from happening by reducing the causes

•  Intervention – Discuss ways to recover from errors when

they do happen


Error identification


Errors people make in taking pictures

•  Wanting to take pictures but taking videos instead

•  Wanting to snap a picture but turning off the camera instead

•  Taking pictures with the lid still covering the lenses

•  Facing the wrong direction •  Sending enormous files by emails •  Covering the lenses by fingers •  Taking pictures with shaky hands •  Not holding the snap button long enough to

trigger a snap


Error classification

•  When? – Perceptual errors – Cognitive errors – Motor errors

•  How? – Mistakes – Failures – Slips and lapses


Perceptual errors

•  Causes: – Misleading perceptual cues – Sensory overload

•  Examples: –  I didn’t notice the battery indicate turns red. –  I didn’t realize these buttons are different. –  I thought this underlined sentence is a link. –  I thought I heard the sound of someone

sending me an IM.


Cognitive errors

•  Causes: – Complex decision process – High load on memory

•  Examples: – The password I remembered was wrong. –  I added the numbers wrong in my head. –  I didn’t know I was in the video mode.


Motor errors

•  Causes: – Unnatural motor movement •  Cross hand

– Similar motor sequences – Pressured for speed – Tricky hand-eye coordination – Special motor skills (typing, hand drawing)


Motor errors

•  Examples: –  I typed the wrong key. –  I pressed the wrong button. –  I double clicked instead of single clicked. –  I checked the wrong box. –  I typed one too many letter. –  I can’t get the mouse to where I want.


Failures

•  Causes: – Know what to do but difficult to do it

successfully

•  Examples: – Putting a thread into the eye of a needle – Looking for a needle in the haystack – Adding numbers in the head – Pulling off a quadruple click


Mistakes

•  Causes: – Do the wrong thing for the goal – Apply a rule in a wrong situation – Make a bad decision

•  Users may not be aware of the mistake •  It can be a learnability or memory issue.


Mistakes

•  Examples: – Sending a gigantic photo via email – Ordering a product from a shady vendor – Deleting files by removing shortcuts from

the desktop – Forgetting to turn cell phones to vibration


Slips and lapses

•  Causes: – Working memory failure – Do something familiar but miss a few steps

•  Slip –  failure of execution

•  Lapse –  failure of memory


•  Unintentional •  Users realize right away •  More common than mistakes •  Slow users down


Six types of slips and lapses

1.  Capture errors 2.  Description errors 3.  Data driven errors 4.  Associate activation 5.  Loss of activation 6.  Mode errors


1. Capture errors

•  A familiar sequence of actions captures an unfamiliar sequence of actions.

•  Examples: – Get off the exit to work prematurely on a

weekend grocery trip – Open up a web browser and find yourself

going to Facebook instead of where you meant to go


2. Data-driven error

•  An automatic action triggered by arrival of sensory info which intrudes into the normal action

•  Parameters in STM wrongly replaced by new sensory info

•  Examples: – Wanting to say X but instead saying Y

because you heard someone nearby yelling Y


3. Description errors

•  Actions have similar descriptions •  When performing one action, one

mistakenly perform a different action that fits the description.

•  Description can be visual, spatial, or semantic.



•  Wanting to maximize a window but instead minimizing it – Description: ?

•  Wanting to save a file but instead opening up the save-as dialog box – Description: ?

•  Wanting to reply to sender but instead reply to all – Description: ?



•  Wanting to maximize a window but instead minimizing it – Description: click on the button at the upper-left

corner (spatial similarity) •  Wanting to save a file but instead opening

up the save-as dialog box – Description: click on the button that looks like a

floppy disk (visual similarity) •  Wanting to reply to sender but instead reply

to all – Description: click on the button for reply

(semantic similarity)


4. Associative activation

•  Internal thoughts and associations trigger the wrong action

•  Wrong reflexes •  Example: – Phone rings yell “come in”. – Dismiss an important message box


5. Loss of activation

•  Forgot the goal in the middle of a sequence of actions performed to fulfill the goal.

•  Examples: – Forgot what we went into the room for. – Forgot why we visited a website – After starting Skype, forgot whom we wanted

to call – Go to Google but forgot want we wanted to

search


6. Mode error

•  Do action in one mode thinking you’re in another.

•  Examples: – Typing password not knowing the Cap Lock

is on – Deleting all files but in the wrong directory. – Typing gibberish in the wrong language

mode.


Exploiting user errors (Bad)

•  Phishing •  Fake anti-virus program •  Internet button next to call button


Activity: What kinds of slips and lapses?

1.  Wanting to take a picture but shooting a video instead

2.  Typing the password in the field for the login name

3.  After installing a software, forgetting why you did it

4.  Clicking on “send” without first attaching a filf 5.  Typing ‘ls’ in a Windows terminal 6.  Closing a popup immediately upon seeing it

and prematurely terminating a process 7.  After seeing a new email notification, typing the

sender’s name in a word document


Error prevention


Tragedy that can be avoided

•  People running down the stairs but found themselves trapped in the basement …


Forcing function

•  Interlock •  Lockin •  Lockout

•  Behavior shaping constraints •  Physical vs. Software


Interlock

•  Force operations to take place in a proper sequence

•  Real-world examples: – Cars that force us to shift to P before we can

turn the engine off

•  UI examples: – ATMs that force us to remove ATM cards

before before we can proceed


Lockin

•  Keep an operation active, preventing someone from accidentally stopping it prematurely

•  Real-world examples •  UI examples: – soft on/off switch


Lockout

•  Require efforts to unlock a feature to prevent accidental access

•  Real-world examples: the stopping bar in the stair to the basement, the safety-pin of a grenade

•  UI examples: – Mac’s lock button


Errors where forcing functions may apply

•  I forgot to remove the cartridge before turning my Nintendo off. –  Interlock

•  I forgot to remove the lid off the lenses before taking pictures –  Interlock

•  I accidentally close the window before the download is completed –  Lockin

•  I accidentally formatted my hard drive. –  Lockout


Errors summary

•  When? (read-scan, think, act) –  Perceptual errors –  Cognitive error –  Motor errors

•  How? (intentional vs. accidental) –  Failures –  Mistakes –  Slips and lapses

1.  Capture errors 2.  Description errors 3.  Data driven errors 4.  Associate activation 5.  Loss of activation 6.  Mode errors


Preventing general errors

Avoid the causes listed earlier …

•  Perceptual – Avoid misleading visual cues

•  Cognitive – Avoid memory load

•  Motor – Avoid unnatural motor movement


Preventing mistakes

•  Hard to do through design – We can’t prevent users from making bad

decisions by intention

•  Possible solutions: – Provide “reasonableness” check – Provide help and documentation


Preventing lapses

1.  Capture errors 2.  Description errors 3.  Data driven errors 4.  Associative activation 5.  Loss of activation 6.  Mode errors


1. Preventing capture errors

•  Avoid habitual action sequences with identical prefixes


2. Preventing description errors

•  Avoid actions with very similar descriptions

•  Keep dangerous commands away from common ones – E.g., save and delete should not be together

•  Provide contrast


3. Preventing data-driven errors

•  Avoid distracting sensory information •  Reduce the need to keep data in the

working memory (so it won’t get replaced)


4. Preventing associative activation errors

•  Avoid similar stimulus or notification for different actions


5. Preventing loss of activation

•  Keep procedures short – so users won’t lose track of the steps

•  Minimize interruptions – so users won’t get distracted and forget


6. Preventing mode errors

•  Eliminate modes or provide visible cues •  Minimize shared actions across modes •  Use spring loaded or temporary modes. – Examples: •  drag-and-drop by holding down mouse button •  batch-selection by holding shift


Confirmation dialog

•  Limitations: – People tend to explain away errors. – Reduces the efficiency – Habitual dismissal reduces its effectiveness

when something serious really happens

•  Examples: – Engine check light – False alarms – Web site security warning


Activity: What kinds of slips and lapses?

1.  Wanting to take a picture but shooting a video instead

2.  Typing the password in the field for the login name

3.  After installing a software, forgetting why you did it

4.  Clicking on “send” without first attaching a filf 5.  Typing ‘ls’ in a Windows terminal 6.  Closing a popup immediately upon seeing it

and prematurely terminating a process 7.  After seeing a new email notification, typing the

sender’s name in a word document


Error recovery


Guidelines

•  Provide undo •  Provide cancel •  For form input errors, help users locate

the fields that need to be fixed •  Provide context-sensitive help •  Comfort the users


Error messages

•  Best error message is none at all •  Be precise •  Restate user’s input •  Speak the user’s language •  Give constructive help •  Be polite, avoid loaded words •  Avoid frivolous error messages


•  The mouse cursor is outside of the visible screen area.

•  A string is typed in the font size selection text field!!

•  Error code = 24 •  Your action has caused the program to

crash.


•  Fatal error saving file •  The file can not be saved. •  There is an error saving “xxx.doc”. •  There is an error saving “xxx.doc”

because of the format. •  There is an error saving “xxx.doc”

because of the format. Please make sure it is an image file.

Lecture 12: Errors - UMD Computer Science Department … · Spring 2010 CMSC 434 Introduction to...

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