CCT384 – Universal Design and Access

CCT384 – Universal Design and AccessUD Principle: Tolerance for Error

Week 3

From previous week

Designing Labs for Peoples with Disabilities

http://www.washington.edu/doit/Video/Wmv/temp/equal.asx

The design minimizes hazards and negative consequences of accidental actions.

Principle 5: Tolerance for Error

Principle 5: Tolerance for Error

The design minimizes hazards and negative

consequences of accidental actions.

“CAUTION: It is not recommended that children or pets regularly drink water from the toilet, even though the bowl water is not harmful to children or pets.”

Label on toilet bowl cleaner bottle

Design of Everyday Things

About Donald A. Norman BS and EECS from MIT

Ph.D. in psychology from UPenn

Centers for Cognitive Studies at Harvard

professor emeritus of cognitive science at UCSD

VP of Advanced Technology Group at Apple; HP

co-founder of Nielsen Norman Group (usability consulting company)

professor of computer science at Northwestern

About the Book

first published in 1988original title: “The Psychology of Everyday Things”

User-Centered Designstructure of tasksmaking things visiblegetting the correct mappingexploiting the powers of constraintdesigning for errorexplaining affordances and seven stages of action.

Slips versus Mistakes Recall:

Human errors can be classified into slips and mistakes

Can understand using Norman’s gulf of execution SLIP: If you understand a system well you may know exactly what to

do to satisfy your goals: you’ve formulated the correct action. But you may fail to execute that action correctly (mis-type, press the wrong button)

MISTAKE: If you don’t 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.

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Errors in User-Computer Dialog Three phases

Read-scan phase -- Perceptual errors Think phase -- Cognitive errors Respond phase -- Motor errors

Can generally lead to either slips or mistakes

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Perceptual Errors Result from poor perceptual cues

Display of objects that are visually similar Invisible or poorly expressed states Failure to capture user’s attention Lack of perceivable feedback

Perceptual Errors 12

Are perceptual errors likely here?

Tallly Ho Uniforms

Cognitive Errors Caused by taxing memory and thinking

Tax recall memory Poor mnemonic aids Inconsistency Lack of context or status info

e.g., where came from in a menu Mental calculations and translations

Cognitive Errors

Are cognitive errors likely here?

Motor Errors Taxing the motor skills

Awkward movements Highly similar motor sequences

e.g., double click, click Pressure for speed Require a high degree of hand-eye coordination Requiring special types of motor skills (type)

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Motor Errors

Lots of errors are likely here!!

Example Studies 170 experienced UNIX users over 9 days

Individual commands error rates of 3-50%

300 security system users over 20 months 12,117 error messages Most common 11 errors -> 65% 2517 involved repeated errors (with no non-errors in

between) within 10 minutes Bad error recovery/help

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Kraut et al, CHI ‘83

Mosteller & Ballas, Human Factors ‘89

Slips Automatic (subconscious) error that occurs without

deliberation

Examples?

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Types of Slips 1. Capture error

Continue frequently done activity instead of intended one Type “animation” instead of animate Confirm deletion of file instead of cancel

2. Description error Intended action has much in common with others possible

(usually when distracted, close proximity) ctrl key & caps lock key / Sun & Mac

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Types of Slips 3. Data driven error

Triggered by arrival of sensory info which intrudes into normal action Call to give someone a number, dial that number instead

4. Associative activation Internal thoughts and associations trigger action

Phone rings, yell “come in”

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Types of Slips 5. Loss of activation

Forgetting goal in middle of sequence of actions Start going into room, then forget why you’re going there

6. Mode errors Do action in one mode thinking you’re in another

Delete file, but you’re in wrong directory

Error-handling Strategies

1. Avoid and prevent

2. Identify and understand

3. Handle and recover

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Preventing Errors Rules 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 metaphor

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Error Prevention Guidelines

Eliminate modes or provide visible cues for modes

Use good coding techniques (color, style)

Maximize recognition, minimize recall

Design non-similar motor sequences or commands

Minimize need for typing

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Error Prevention Guidelines

Test and monitor for errors and engineer them out

Allow reconsideration of action by user (e.g., removing file from trash)

Error Prevention Guidelines Provide appropriate type of feedback

Gag - Prevent user from continuing Erroneous login

Error prevention

Warn user an unusual situation is occurring Bell or alert box

Error prevention

Nothing - Just don’t do anything (Careful, user must determine problem) Mac: move file to bad place

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Error Recovery Guidelines

Provide undo function!

Provide cancel function from operations in progress

Require confirmation for drastic, destructive commands

Provide reasonableness checks on input data Did you really mean to order 5000?

Fall 2006PSYCH / CS 6750

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Error Recovery Guidelines However, before a user can recover, must be able to detect that an error

has occurred Detection: provided by easy visibility, feedback

Other options? Self-correct - Guess correct action & do it

Spell-check correction Dialog - System opens dialog with user

Go into debugger on run-time crash

Query - Ask user what should’ve been done, then allow error action as legal one (“did you mean…?”)

Command language naming error

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Error Recovery Guidelines Return cursor to error field, allow fix

Tell them what to fix, how to fix it

Provide some intelligence Guess what they wanted to do

Provide quick access to context-sensitive help

Fall 2006PSYCH / CS 6750

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Error Handling Example (Web) Form fill in is the most common error case

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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

Command Assistance E.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 information

But… What if people don’t know what they’re 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.

Context-sensitive Help Move away from placing onus on user to remember the

command

Often not very sophisticated

Common examples: Microsoft’s “What’s This?” option Tooltips Clippy (arrrgh…)

What’s the “context”? Just the control itself? (Simple) User’s past history and application state? (More sophisticated)

Wizards and Assistants Attempt to prevent errors by providing “common paths” through

software Safety, efficiency, and accuracy (as long as it’s a supported task)

May be unnecessarily constraining

Guidelines: allow backward movement, show progress indicator

Assistant: Clippy is actually an example of this. A context-sensitive trigger to launch a wizard style interaction

Q: What went wrong with Clippy?

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Mistake-proofing: a preliminary definition

Mistake-proofing is the use of process design features* to facilitate correct actions, prevent simple errors, or mitigate the negative impact of errors.

Mistake-proofing tends to be inexpensive, very effective, and based on simplicity and ingenuity.

It will not make processes free of all errors, nor is it a stand-alone technique that will eliminate the need for any other responses to error.

*these process design features will be referred to as “devices” or “counter-measures”

Design

…Then the methods of reducing risks and hazards are limited to: What can be put on paper and subsequently… What can be embedded in the human brain.

“Knowledge in the head”*

*Source: Donald Norman, The Design of Everyday Things

Design “human errors can be made irrelevant to outcome,

continually found, and skillfully mitigated.”

Can human errors become irrelevant by only changing knowledge in the head?

“Knowledge in the World”*

*Source: Donald Norman, The Design of Everyday Things

To err is human

Have you ever gone somewhere and not remembered why you went there?

Have you ever gone home when you meant to stop at a store?

Why does that happen? How would you prevent it if your life depended on it?

“Be more careful” not effective “The old way of dealing with human error was to scold people,

retrain them, and tell them to be more careful … My view is that you can’t do much to change human nature, and people are going to make mistakes. If you can’t tolerate them ... you should remove the opportunities for error.”

“Training and motivation work best when the physical part of the system is well-designed. If you train people to use poorly designed systems, they’ll be OK for awhile. Eventually, they’ll go back to what they’re used to or what’s easy, instead of what’s safe.”

“You’re not going to become world class through just training, you have to improve the system so that the easy way to do a job is also the safe, right way. The potential for human error can be dramatically reduced.”

Chappell, L. 1996. The Pokayoke Solution. Automotive News Insights, (August 5): 24i. LaBar, G. 1996. Can Ergonomics Cure ‘Human Error’? Occupational Hazards 58(4): 48-51.

A new attitude toward preventing errors:

“Think of an object’s user as attempting to do a task, getting there by imperfect approximations. Don’t think of the user as making errors; think of the actions as approximations of what is desired.”*

*Source: Norman, The design of everyday things. Doubleday 1988.

These approximations are part of Norman’s concept of “knowledge in the head”

A New Attitude toward Preventing Errors

Make wrong actions more difficult

Make it possible to reverse actions — to “undo” them—or make it harder to do what cannot be reversed.

Make it easier to discover the errors that occur.

Make incorrect actions correct.

These outcomes do not occur without design changes

Precise outcomes without precise knowledge or action?

Provide clues about what to do: natural mappings affordances visibility feedback constraints

Natural Mappings: Which dial turns on the burner?

Stove A

Stove B

Affordances: How would you operate these doors?

BA C

Push or pull? left side or right? How did you know?

Affordances: How would you lift this pan?

“SUPPORT THE BOTTOM”

Visibility and Feedback Visibility means making relevant parts visible, and

effectively displaying system status

Feedback means providing an immediate and obvious effect for each action taken.

Constraints: How would you assemble these parts?

Interdisciplinary Approach to Design

Psychology:

Norman recommends designing forcing functions into process: “actions are constrained so that failure at one stage prevents the next step from happening.” “[they] rely upon properties of the physical world for their operation; no special training is necessary”.

“Knowledge in the Head”vs. “Knowledge in the World”

Designing Benign Failures

Quality Management:

Shingo recommends that “when abnormalities occur, shut down the machines or lock clamps to halt operations thereby preventing the occurrence of serial defects.”

With “the idea of discovering errors in conditions that give rise to defects and performing feedback and action at the error stage so as to keep those errors from turning into defects.”

What is Poke-yoke?

A method that uses sensor or other devices for catching errors that may pass by operators or assemblers. 1. Control Approach - Shuts down the process when an error occurs. - Keeps the “suspect” part in place when an operation is incomplete.2. Warning Approach - Signals the operator to stop the process and correct the problem.

Introduction

Shigeo Shingo invented the Japanese concept called Poka-Yoke (pronounced POH-kah YOH-kay)

Poka-Yoke means to mistake proof the process The essential idea of poka-yoke is to design your

process so that mistakes are impossible or at least easily detected and corrected

First Poka-Yoke Device Shingo suggested a solution that became the first

Poka-Yoke device In the old method, a worker began by taking two

springs out of a large parts box and then assembled a switch

Problem: Sometimes the worker failed to put both springs in the switch

In the new approach, a small plate is placed in front of the parts box and the worker's first task is to take two springs out of the box and place them on the plate Then the worker assembles the switch. If any spring

remains on the plate, then the worker knows that he or she has forgotten to insert it

The new procedure completely eliminated the problem of the missing springs

Empty plate

First Poka-Yoke Device

Categories of Poka-Yoke Poka-yoke devices fall into two major categories:

Prevention Detection

A prevention device engineers the process so that it is impossible to make a mistake at all

A classic example of a prevention device is the design of a 3.5 inch computer diskette

Impossible to put in upside down

Prevention Example

Categories of Poka-Yoke A detection device signals the user when a mistake

has been made, so that the user can quickly correct the problem

My car beeps if I leave the key in the ignition

Detection Example

Locking devices on filing cabinet prevents opening multiple drawers which would lead to tipping

Other Poka-Yoke Examples

Gas pumps are equipped with hose couplings that break-away and quickly shut-off the flow of gasoline

Other Poka-Yoke Examples

This rental truck has a door latch which will not allow the loading ramp to slide out while the latch is in the closed

position

Other Poka-Yoke Examples

The Saf-T-Smart valve kit detects when the washing machine is operating and opens the valves allowing water to flow freely. When the washing machine is off the valves are closed, reducing pressure on the hoses and avoiding serious water damage (and returning to a flooded house).

Other Poka-Yoke Examples

The U.S. Consumer Product Safety Commission has recorded 105 deaths that were caused by wheelchairs rolling away from the person.The response? A mistake-proofing device that locks the wheelchair when no one is sitting in it. An unlocking lever on the handle allows the wheelchair to be moved when empty.

Other Poka-Yoke Examples

When pipes are likely to freeze, the common practice is to open faucets slightly and let them drip.

This device automatically opens a valve that discharges just enough water to avoid pipes freezing.

Other Poka-Yoke Examples

Other Poka-Yoke Examples Limit switches

Interlocks

Jigs

Alignment marks

Go/no-go devices

Electronic eyes

Checklists

Summary

Poka-Yoke means to mistake proof the process Remove the opportunity for error

Improve the process Make wrong actions more difficult

If you can’t remove the opportunity for error Make it easier to discover the errors that do occur

This is not about punishing workers

Mistake proofing recognizes that every human will make mistakes and tries to set up systems that minimize or eliminate those mistakes.

Causes of Human Errors in Computer Systems

1. Personal factors (35%): Lack of skill, lack of interest or motivation, fatigue, poor memory, age or disability

2. System design (20%): Insufficient time for reaction, tedium, lack of incentive for accuracy, inconsistent requirements or formats

3. Written instructions (10%): Hard to understand, incomplete or inaccurate, not up to date, poorly organized

4. Training (10%): Insufficient, not customized to needs, not up to date

5. Human-computer interface (10%): Poor display quality, fonts used, need to remember long codes, ergonomic factors

6. Accuracy requirements (10%): Too much expected of operator

7. Environment (5%): Lighting, temperature, humidity, noise

Because “the interface is the system” (according to a popular saying), items 2, 5, and 6 (40%) could be categorized under user interface

Causes of Human Errors in Computer Systems

Properties of a Good User Interface1. Simplicity: Easy to use, clean and unencumbered look

2. Design for error: Makes errors easy to prevent, detect, and reverse; asks for confirmation of critical actions

3. Visibility of system state: Lets user know what is happening inside the system from looking at the interface

4. Use of familiar language: Uses terms that are known to the user (there may be different classes of users, each with its own vocabulary)

5. Minimal reliance on human memory: Shows critical info on screen; uses selection from a set of options whenever possible

6. Frequent feedback: Messages indicate consequences of actions

7. Good error messages: Descriptive, rather than cryptic

8. Consistency: Similar/different actions produce similar/different results and are encoded with similar/different colors and shapes

Everyday Examples

New lawn mowers are required to have a safety bar on the handle that must be pulled back in order to start the engine. If you let goof the safety bar, the mower blade stops in 3 seconds or less.

Fueling area of car has three error-proofing devices: 1. insert keeps leaded-fuel nozzle from being inserted 2. tether does not allow loss of gas cap 3. gas cap has ratchet to signal proper tightness and prevent overtightening.

3.5 inch diskettes cannot be inserted unless diskette is oriented correctly. This is as far as a disk can be inserted upside-down. The beveled corner of the diskette along with the fact that the diskette is not square, prohibit incorrect orientation.

Activity

Applying Universal Design – from learning to practice

Class Exercise

Each table or group is to list other examples of Poka-Yoke (mistake proofing) devices

Brainstorming!!

Class ExerciseMistake-Proof This:

A local countertop company makes and then loads the countertop pieces on to a truck and goes to the customer’s home and installs the countertop. More than 15% of all installation jobs have to be done with more than one trip to the customer’s home because one or more pieces of the countertop was not loaded on the truck.Propose a change that will ensure all the material is loaded on the installation truck.

Class Exercise

Mistake-Proof This:

Mechanics in the instrument lab have to calibrate instruments in accordance with a procedure that has several steps. They sometimes inadvertently skip a step in the procedure.

Propose a change that will ensure no steps are skipped.

Class Exercise

Mistake-Proof This:

The far-sighted instructor in a rush to get to work on time often forgot and left his glasses at home.

Propose a change that will ensure the instructor does not forget his glasses.

References The Principles of Universal Design‚ Version 2.0 (1997) by North Carolina State University (as

cited in Preiser & Ostroff ‚ 2001)

Center for Universal Design (US) Home of the Principles of Universal Design, Exemplars of Universal Design, universal design history, the Design File, Center for Universal Design Newsline, publications, and more. http://www.design.ncsu.edu/

CAST (US) Home of Bobby, the web accessibility analysis tool, Universal Design in Learning and the National Center On Accessing the General Curriculum, and eProducts. http://www.cast.org

DO-IT: Disabilities, Opportunities, Internetworking, and Technology, http://www.washington.edu/doit/

Adaptive Environments Center (US) Home of the South Boston Waterfront Project, Designing for the 21st Century Conference, Access to Public Schools, New England ADA Technical Assistance Center, universal design education and consulting, Access to Design Professions, publications and more. http://www.adaptenv.org

Accessible Electronic & Information Technology: Legal Obligations of Higher Education and Section 508, Cynthia D. Waddell, J.D., 1999, http://athenpro.org/node/54

Next class Next class: Universal Design Principle: Perceptible

Sound

Readings: Erlandson, Chapter 7