1. Norman Chapter 5 Error Messages and Other Feedback
Jeff Offutt, updated by Paul Ammann
SWE 205
Software Usability and Design

2. Human Error Inspector General/Airforce interaction
AF: It was pilot error – the pilot failed to take corrective action
IG: That’s because the pilot was probably unconscious
AF: So you agree, the pilot failed to solve the problem
Why does it matter from an engineering perspective if “human error” is the diagnosis?
What was the human asked to do?
What happens next time?
It’s really important to understand what humans actually do!
5-Apr-19
© Offutt

3. Root Cause Analysis Why did something (bad) happen?
Often a difficult question to answer
Asking the “why” questions recursively
The swiss cheese model
Accidents usually have many factors
Hazard analysis
Hazards can (often) be identified and controlled
Accidents are inherently unpredictable
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4. Two Kinds of Errors Norman distinguishes:
Slip: Intends one thing, but does something else
Forgot to turn off the stove
Closed a window with a keyboard shortcut while intending to type text (and discarded work)
Mistake: Wrong goal or plan
Used the dishwasher to cook dinner
Closed the wrong window (and discarded work)
The distinction matters for usability
Think about the pop-up for the two window examples
Note that keyboard shortcuts are mode systems
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5. Slip Classification Capture slips Description-similarity slips
Hand back graded work; continue with just-handed in work
Description-similarity slips
Work the wrong light switch
Memory-lapse slips
Use ATM; walk away without card (or money?)
Mode-error slips
In “vi”, you think you’re in “input” mode
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6. Errors and Safety Checklists
Are they better with slips or mistakes?
Why are they used sometimes but not others?
Error reporting – what to do after an error is made?
Are errors punished?
If so, under what circumstances?
Human error
What does that mean?
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© Offutt

7. Mistake Classification
Rule-based mistakes
With anti-lock brakes, is driver intervention required?
Knowledge-based mistakes
What to do in a novel situation
Memory-lapse mistakes
Often driven by interruptions!
Operator loses context, and proceeds with wrong plan
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8. Designing for Errors
Understand causes for error and design to minimize them
Make all actions undoable
Make it easy to discover errors (visibility)
Make it easy to correct errors
Do not think in terms of “users making errors,” think in terms of users getting close
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9. we cannot take the next step
Forcing Functions
If we fail at one step,
we cannot take the next step
Examples :
Cannot take the key out of the ignition unless the car is in park
Cannot click Bold unless text is highlighted
Cannot fill out a form unless password is correct
Seatbelts :
Seatbelt automatically engaged when the car started (*choke*)
Car would not start if seatbelts are not engaged
Car buzzes or dings for 2 minutes if seatbelts not engaged
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10. Other Safety Constraints
Interlocks : Users cannot reach step i unless step i-1 was completed
Microwave doors
User agreements in software installations
Lockin : Users cannot stop in mid-operation
Gmail won’t let us leave in the middle of an action
Lockout : Users cannot go to a dangerous place
Stairs to basements are barred to send people out the first floor in a fire
Safety & security constraints vs. usability
Designers must minimize the impact
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© Offutt

11. Three General Principles for Error Message
Be specific
Give constructive guidance in a positive tone
Use a user-centered style
These are also good leadership tips
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© Offutt

12. A message that has to be explained has failed
(1) Be Specific
A message that has to be explained has failed
Users should not have to read a message twice
Messages should be concise, informative, and in the users’ vocabulary
A useful message should state:
What error has been detected
Which input field contains the error
and most importantly …
What corrective action to take
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13. (1) Be Specific Examples Non-specific Specific Invalid input
The id number must be 5 numeric digits
Invalid date
Format: MM/DD/YY
SYNTAX ERROR
Unmatched left parenthesis
Illegal entry
Type first letter: Send, Read, or Drop
Error accessing
SOCKET: Connection
refused
is busy, try again later
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14. (2) Give Constructive Guidance in a Positive Tone
Meaningful messages
Positive tone
Not incriminating
Blame system, not users
State what should be there,
not what should not
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15. (2) Give Constructive Guidance in a Positive Tone
Examples
Non-constructive
Constructive
Illegal year!
The year must be between 1995 and 2015.
Your id # has characters !
The id # must be numeric. Please re-enter.
Part Code not numeric.
Part Code must be 3 numeric digits.
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© Offutt

16. (3) Use a User-Centered Style
Messages should be:
In the user’s vocabulary
Courteous
Not Imperative
Examples
Non-user-centered
User-centered
ENTER DATA.
Ready for command:
Ready!
Your turn :
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17. Example
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18. Example
I did!
Maybe I need 50 cents … 50
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19. Example Must enter 2 zeros (other values not allowed) 00 50 5-Apr-19
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20. Example
This modal dialog box will not allow me to see the message (with crucial info!) while editing the slides. I have to respond before editing.
5-Apr-19
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21. Examples
! HT ACCESS: Error accessing “ “HTTP: File/directory does not exist”
The requested URL /offutt.html was not found on ...
!PrintMonitor is currently printing “Doc 1: Bad Examples” from “WordPerfect 2.1”. If PrintMonitor quits now, “Doc 1: Bad Examples" will be printed when the system is restarted with MultiFinder. Do you want to finish printing before PrintMonitor quits? (Windows 95)
Currently printing. If shutdown occurs now, the document will not be printed until MS Word restarts. You can still delay shutdown until the document finishes printing.
Wait and shutdown after printing:
Shutdown now and cancel printing:
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22. Another Example
: Microsoft OLE DB Provider for ODBC Drivers error ' '
[Microsoft][ODBC SQL Server Driver][SQL Server]Your transaction (process ID #85) was deadlocked with another process and has been chosen as the deadlock victim. Rerun your transaction.
/script/webkatalogen/pb.asp, line 221
Internal failure, please try again.
5-Apr-19
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23. Another Example Bus error, core dumped (Unix)
Access through a nil pointer in function GetNext()
Terminating thread, due to a stack overflow problem. A VxD, possibly recently installed, has consumed too muhc stack space. Increase the setting of MinSPs in SYSTEM.INI or remove recently installed VxDs. There are currently 5 SPs allocated. (Windows 2000)
???
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24. Yet Another Example From Lotus notes What does that mean ??? 5-Apr-19
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25. A Confusing Example
This webpage has a redirect loop. The webpage at has resulted in too many redirects. Clearing your cookies for this site may fix the problem. If not, it is possibly a server configuration issue and not a problem with your computer. Here are some suggestions: Reload this web page later. Learn more about this problem. More information on this error Below is the original error message Error 310 (net::ERR_TOO_MANY_REDIRECTS): There were too many redirects.
5-Apr-19
© Offutt

26. A Commonly Occurring Example
Most browsers give a warning before submitting POST data for the second time
Avoid duplicate submissions and updates
Avoid duplicate purchases
Users should be very careful before overriding this hesitation
However … how many users understand “POSTDATA”?
5-Apr-19
© Offutt

27. Last (Negative) Example
Program Error: WINWORD.exe has generated errors and will be closed by Windows. You will need to restart this program. An error log is being created. (Word 2000)
I got this message, intermittently, for several months before diagnosing the problem
It occurred when I started MS Word (and PowerPoint) … sometimes … and they immediately exited
Restarting the computer did not work
I took my computer to the support center, but they couldn’t get the problem to repeat
The actual problem …
The default printer is a network printer and is currently unavailable. Word is continuing, but you will not be able to print.
5-Apr-19
© Offutt

28. An Outstanding Example
ERROR Forbidden
The server understood the request, but is refusing to fulfill it.
Authorization will not help and the request SHOULD NOT be
repeated. This status code is commonly used when the server does
not wish to reveal exactly why the request has been refused, or
when no other response is applicable.
Having trouble? Maybe one of these links will help you find what
you are looking for: Hardware, Software, Solutions, Storage
Systems Products.
Search:
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29. Another Outstanding Example
From Thunderbird mailer, when it finds the string “attach” in an message, but no attachment:
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30. An Interesting Example
Command: Mail To: fred
Subject:
No subject – Continue with message? (y/n) n ___
Interesting escape
A reminder that we should use subject lines.
Intrusive or protection?
5-Apr-19
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31. A Stupid Example
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32. Another Stupid Example
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33. Philosophy of Designing for Errors
Think of the user’s point of view
Assume every mistake will occur
Make every action reversible
Put the required knowledge in the world
But provide shortcuts for users who have knowledge in their heads
Use syntactic constraints as much as possible
Selection vs. typing
Make the results of actions obvious
If possible, make them obvious before actions are committed
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© Offutt

34. Summary Good Error Messages: Increase speed of use
Increase subjective satisfaction
Reduce repeat errors
5-Apr-19
© Offutt