What is usability?
ISO 9241
Usability is a measure of the effectiveness, efficiency and satisfaction with which specified users can achieve specified goals in a particular environment.
Key terms in the ISO 9241 definition
- Effectiveness, efficiency, satisfaction
- Specified users, specified goals, particular environment
The five Es of usability
Effective
- Completeness - was the task fully completed? Were the user's goals met?
- Accuracy - was the task completed successfully? Did the user get the right or correct result? How well was the work done?
Efficient
- Speed - was the user able to complete the task quickly?
- Effort - was the user able to complete the task without undue cognitive effort?
Engaging
- Pleasant - did the user have a pleasant experience when working on the task?
- Satisfying - was the user satisfied by the way in which the application supported her work?
Error tolerant
- Error prevention - did the user interface help users avoid making errors? Were errors minor rather than major?
- Error recovery - if the user made an error, did the interface assist them in making a successful recovery?
Easy to learn
- Predictability - was the user able to work with some certainty because the user interface built on her previous knowledge?
- Consistency - was the interface consistent, so that once a user learnt how to use part of the application, they were able to easily learn how to use another part?
References
- Definition of usability
- Usability basics
- What does usability mean: looking beyond 'ease of use'
- User-centred design standards
History of usability
Usability comes from the field of human factors
- Concept of usability comes from the field of human factors
- Human factors (also known as 'ergonomics') has its roots in psychology (now multidisciplinary)
- Human factors methods and practices originated within the US military during World War 2
- Sophisticated weaponry had to be usable
- If it couldn't be used, military objectives could not be met
- If it was used incorrectly, would kill the forces using it rather than the enemy
What is human factors?
- Study of human beings
- Focus is on understanding the advantages and limitations of the human body and mind
- Focus also on how human performance is affected by environmental factors
What are the goals of human factors?
- Basic operational objectives
- Reduce errors
- Increase safety
- Improve system performance
- Objectives bearing on reliability, maintainability,
and availability (RMA), and integratied logistic support (ILS)
- Increase reliability
- Improve maintainability
- Reduce personnel requirements
- Reduce training requirements
- Objectives affecting users and operators
- Improve the working environment
- Reduce fatigue and physical stress
- Increase human comfort
- Reduce boredom and monotony
- Increase ease of use
- Increase user acceptance
- Other objectives
- Reduce loss of time and equipment
- Increase economy of production
Multidisciplinarity of human factors
- Psychology
- Human sensory capacities
- Human memory and cognitive processes
- Individual differences and their measurement
- Anthropometry
- Concerned with the measurement of the physical features of people
- Used in the design of seats, chairs, tables, computer consoles, automobile interiors, aeroplane, cockpits, and many other work stations
- Environmental medicine
- Concerned with environmental factors and their effects on health and human performance
- Engineering
- Provides with information on electrical, mechanical, and chemical characteristics of elements and systems and principles of design, construction and operation of structures, equipment and systems
- Statistics
- Used for summarising large amounts of data on human measurements and human performance
- Also used to design sampling schemes and experiments for the conducct of human studies and performance measurements
- Industrial design
- Concerned with design, colour, arrangement, and packaging to combine functionality and an aesthetically satisfying appearance
- Computing
- Human-computer interaction is concerned with human factors relevant to interactions with computers and software applications
References
- Introduction to Human Factors (lecture)
- History of the Human Factors and Ergonomics Society
- 50 Years of Human Engineering - History and Cumulative Bibliography of the Fitts Human Engineering Division
Some examples of poor usability
Usability--good or poor--is all around us
- We experience different degrees of usability when we use the objects in our everyday environment
- We're more likely to remember poor usability than good usability
- Here are some examples
How do I turn this computer on?
About
4 or 5 years
ago I'd just started a new job- I had a choice of using a fairly new Macintosh or a rather old PC - I wanted to use the Mac
- I'd never used a Mac before
- And I couldn't figure out where the "ON" switch was
- After messing around for a long time, I reluctantly sought advice from a colleague in the next office
- He couldn't figure out how to turn it on either
- Finally, we accidentally turned it on after randomly pressing a whole bunch of keys on the keyboard
- We still didn't know how we'd done it, so we turned it off and tried the keys again until we realised it was the Apple key that brought the machine to life
Did I send that fax?
- A couple of years ago, the department I worked in bought a new multi-function office machine
- I wanted to send a fax, so I loaded the document and dialled the number
- Then I was disturbed by a colleague who'd come in to collect a print job
- I couldn't recall hearing the machine dialling and nothing appeared on the control panel to indicate that anything had happened
- So I tried again
- Again I was disturbed in the process
- Again the machine didn't give me any feedback (aural or visual) to indicate that it had sent the fax
- So I tried a third time
- This time I wasn't interrupted and noticed a small green light marked "Comm" go on
- I was reasonably confident that something had happened
- When I got back to my desk, the person I'd been trying to send the fax to rang to tell me "thanks for sending the fax--three times"
Which burner on the cooktop is which?
- A lot of cooktop controls are difficult to use
- This one pictured below is no exception
- Can you work out which control operates the bottom left burner?
- Compare this second stove top
- It's easy to work out which control operates which burner
Trapped between two doors
- This set of doors connects a walkway between two buildings
- You pull the handles on the first set of doors to enter the walkway
- Many people pull the handles at the next set of doors thinking the doors will open
- Some people have been trapped between these sets of doors for a while until they figure it out
- Although both sides of both sets of doors have handles, only the outer handles are meant to be pulled
- Using either set of doors once inside the walkway, to exit, one needs to push
How do I open the refrigerator?
- This refrigerator was purchased for a staff room
- Many people tried to open it using the recessed handles shown in the photo
- Some pulled so hard they moved the fridge, but still couldn't open the door
- Another set of recessed handles were on the right side of the fridge
- The fridge opened from the right side
- Recesses were provided on both sides to allow the door to be hinged on either side
References
- See Bad Human Factors Designs for many more examples
Design principles
Visibility - the Macintosh example
- One of the most important design principles is visibility
- Visibility is achieved by placing the controls in a highly visible location
- Designing for visibility means that just by looking, users can see the possibilities for action
- Visibility is often violated in order to make things "look good"
- Visibility problems come in many forms - and some of the principles discussed below show how visibility can be improved
Feedback - the fax example
- Feedback is the provision of information to a user about the result of
an action
- The tone on the telephone touchpad provides audible feedback to indicate that it has registered the key push
- Web browsers provide a "connecting to..." or similar message to indicate they are going off to retrieve the page you requested
- A indicator light usually flashes when you activate a turn signal in your car
- When feedback is used in design, the system tells the user that it has done something in response to the user's input
Natural mapping - the cooktop example
- Mapping is the relationship between controls and their action or effect in the world
- Natural mapping takes advantage of physical analogies and cultural standards
to provide the user with an understanding of how something works
- The layout of the cooktop controls utilises natural mapping when it matches the layout of the burners
- The operation of a car's steering wheel is analogous to the direction in which the car will turn
- A set of left- and right-pointing arrows on a web page use a physical analogy to indicate backward and forward movement. The labels "back" or "previous" and "next" would be redundant
Affordances - the door handle example
- Affordances are properties of an object that indicate how it can be used
- Chairs afford sitting
- Buttons afford pushing
- Handles afford pulling (as in our door example above)
- Knobs afford turning
- Slots afford insertion of suitably shaped/sized objects
- When affordances are used in design, users know how to use the object just by looking
Constraints - the refrigerator and door handle examples
- Constraints are properties of an object that limit the ways in which
it can be used
- Jigsaws puzzle pieces utilise shape as well as the printed picture/pattern to provide constraints
- The design of floppy disk drives (1.44Mb) allow the disk to be inserted in the correct way only
- When constraints are used in design, we reduce the possibility of users making errors
Some additional things to consider when designing products for people to use
Conventions
- Often, design practices become conventions because they work well
- Breaking conventions in these kinds of situations leads to products or systems that don't work so well
- The photo above shows a glass door to a restaurant. The top half is clear glass and the bottom is frosted. The door handle is placed right in the middle, making it difficult to get sufficient leverage to pull the heavy door open
- When conventions are used, people can quickly learn how to use the system because of their previous exposure to similar things
- When they are not, people can become quite confused about how a system, product or object works
- The photos above show a water tap in a camping area. The tap has a lever-style operation, where down is off and up is on. However, many people who used it thought they had to pump the lever to make the tap work. A more conventional design would have avoided this confusion
Context of use
- Products or systems may be more or less usable depending on the context in which they are used
- The photo above shows shiny smooth tap handles in a hotel bathroom. With soapy wet hands it is impossible to get a grip on the handle to adjust the water flow
- People may know how to use something, or misunderstand its purpose depending on the context in which they encounter it
- The photo above shows a bathroom in a restaurant. There is a toilet, and in the corner on the floor, a sink. The sign over the sink reads "this is a mop sink", so you can guess how it might have been mistakenly used
Human behaviour
- We should always design to fit human behaviour
- Designs that try to change human behaviour are likely to fail
- The photos above show how garden designers tried to get people to use paths, but how their efforts failed
References
The role of the designer
- The web has changed they way in which we do business
with our clients
- We cannot communicate face-to-face to find out what the client wants
- We cannot do the task or find the information that the client wants
- The web is self-service
- Our web site has to be designed to take the place of the customer service representative
Norman's idea of the "system image"
- So, the role of the designer is to design an interface that tells the user how the system works
- Norman refers to the products of design as the "system image" which includes the user interface, online help and documentation such as user manuals
- The system image must accurately reflect the design model (what the designer knows)
- The system image must also cause the user to form the correct user model (or "conceptual model")
Conceptual models
- A conceptual model (or mental model) is a set of beliefs about the way the system works
- We can also think of a conceptual model as a mental picture or simulation
- If we form an incorrect conceptual model, we may have problems using the system
- Designers need to design to ensure that the design helps the user form
the correct conceptual model
A good conceptual model allows us to predict the effects of our actions. Without a good model we operate by rote, blindly…
Donald Norman, The Design of Everyday Things
An example of the formation of a poor conceptual model
- I needed to travel by train from Cheltenham to Caulfield for a meeting
- I didn't have a timetable, so needed to look it up online
- The image below shows the Victrip homepage with the link "Locate your timetable using the Timetable Finder" highlighted
- On the next screen (shown below), it looked fairly clear that I had to
do four things
- Select the suburb I was leaving from (Cheltenham)
- Select the suburb I want to go to (Caulfield)
- Select the mode of transport (train)
- Press the Go buttom
- So that is what I did (as shown in the screenshot below)
- And then I got this unexpected result
- The screenshot below shows the error message I received: "No matches have been found for timetables that travel directly from your origin suburb. Please click here to display all the timetables that travel through your origin suburb and all the timetables that travel through your destination suburb"
- This is not at all the result that I expected
- The conceptual model I had formed--from looking at the user interface--led me to believe that the system would return a timetable for trains running (on the Frankston line) between Cheltenham and Caulfield
Norman's basic theory of human action
- Having even the most basic understanding of how people do things can help us design better user interfaces
- Norman's theory of basic action can help here
- Three basic stages:
- Goal formation (travel to Caulfield by train)
- Execution (check the timetable by making the relevant selections)
- Evaluation (see the results of my actions)
Seven stages of action
- Norman's theory can be expanded to include 7 stages
- Goal
- Forming the goal
- Execution
- Forming the intention
- Specifying an action
- Executing an action
- Evaluation
- Perceiving the state of the world
- Interpreting the state of the world
- Evaluating the outcome
| Stage of Action | Design Question: How easily can the user...? |
|---|---|
| Forming the goal | Determine the function of the product or system |
| Forming the intention | Tell what actions are possible |
| Specifying an action | Determine mapping from intention to action |
| Executing the action | Perform the action |
| Perceiving the state of the world | Tell if the system is in the desired state |
| Interpreting the state of the world | Determine the mapping from system state to interpretation |
| Evaluating the outcome | Tell what state the system is in |
Gulfs of execution and evaluation
- Gulf of execution: the distance between the user's goals
and the means of achieving them through the system
- When problems in the execution phase occur, the "gulf of execution" widens
- Here, the distance between the users' goals and their ability to use the system increases
- Some examples:
- "What do I do now?"
- "How do I [...]?"
- "I wanted to [...], but I can't see how I would do that?"
- "Do I press this?"
- "Do I type this in here?"
- "I'm looking for [...] but I can't find it"
- Gulf of evaluation: the amount of effort required to determine the system
state
- When problems occur in the evaluation phase, the "gulf of execution" widens
- Here, the distance between the system response and the users' goals widens
- Some examples
- "What happened then?"
- "What did I do wrong"
- User repeats the action (e.g. clicks the NEXT or SUBMIT button)
- Question: which gulf opened up when I could not get my train timetable?
References
Human behaviour on the web
- As designers of web sites and applications, we need to design to fit human behaviour - remember the footpath example?
- It is foolish to design without understanding how people behave
- It is risky to design in a way that ignores human behaviour or tries to change it
The paradox of the active user
- Research conducted at IBM in the early 1980s by Carroll and Rossom
- Found that users wanted to get the job done
- Users were not interested in reading the manuals or studying the system
- Paradoxical because reading the manuals and learning more about the system would make them more proficient users
Larson's dog effect
- A similar kind of behaviour to that observed by Carroll and Rossom has been observed in the way people use the web
- This has sometimes been referred to as "Larson's dog effect"
- Reference is to the Larson cartoon where the man is trying to chastise his dog, but the dog only hears what it wants to hear (its name, Ginger)
- The image below shows an online order form with all the relevant information - name of the object to order, price, ordering options, security for credit card orders and delivery times
- The second form shows what users are likely to read - the price - and then they'll jump in to fill in the text input boxes
A note about download/response times
- Users still expect web pages to load quickly
- User complain at even the smallest delays
A note about "interactivity" on the web
- The excuse I've often heard for the use of animations, such as Flash, is "we wanted to make the site more interactive"
- Yes, users want to interact with your site
- Generally this means they want to get what they came for as fast as they can
- Throwing obstacles in their path is not the kind of interactivity the user has in mind
- "Interactive" does not equal slow loading animations/movies where the user must passively wait for everything to download
"Attention economics"
One of the great ironies of information economics is that while information can be trivially copied and the information bandwidth continues to widen, the individual's attention bandwidth is as narrow as ever
Source: Wired Magazine
- The scarce resource in the information age is attention
- Everyone is suffering from information overload
- There is so much information available to people, that they ignore anything that is not of relevance or interest
How people read online
- Studies by John Morkes and Jakob Nielsen in 1994 and 1997
- Showed users were overwhelmed by large amounts of information on a screen
- "All users complained when they retrieved pages with a screen or more of unstructured text"
- Showed less than 20% of users read online text word by word
- Most users (around 80%) scan text
- Where text was written to be concise, easy to scan and used objective language, usability improved by between 125% and 159%
References
- The Paradox of the Active User (PDF format)
- Humans - A Designer's Guide
- The Attention Economy and The Net
- Writing for the Web