Lecture 8: Usability & Usability Engineering

USABILITY

“Usability: the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use.”

Why is usability important?
-It makes the difference between performing a task accurately and completely or not, and enjoying the process or being frustrated.
-Determine the success or failure of a system
Poor usability…
-Reduce productivity
-Increase cost time and effort

Usability usually refers to software but is relevant to any product. Some ways to improve usability include:
shortening the time to accomplish tasks,
reducing the number of mistakes made,
reducing learning time,
and improving people's satisfaction with a system.

According to Jakob Nielsen (2003), usability is
defined by 5 quality components :

Learnability : ease of learning for novice users.
Efficiency : steady-state performance of expert users.
Memorability : ease of using system intermittently for casual users.
Errors : error rate for minor and catastrophic errors.
Subjective Satisfaction : how pleasant the system is to use.

LEARNING CURVES
Some systems are designed to focus on learnability.

Others emphasise efficiency for proficient users.

Some support a combination of ease of learning and an “expert mode” (for example rich menus and dialogues plus a command/ scripting language)

DOMAIN AND EXPERTISE


RELATIONSHIP BETWEEN USABILITY GOALS AND USER TYPES

Novice Users:
No or limited knowledge of the occupational task to be performed, and of computers and interface concepts or
Knowledge of the occupational task to be performed, and of computers and interface concepts

Knowledgeable Intermittent Users:
Understanding of the task concepts
Broad knowledge of computers and interface concepts.
Intermittently use the system and may therefore have problems with retention

Expert Frequent (Power) Users:
Thoroughly familiar with both task and interface concepts. They are likely to use the system often and appreciate short cuts to speed their work.

TYPICAL WAYS OF MEASURING USABILITY

Learnability: pick novice users of system, measure time to perform certain tasks.
Distinguish between the various timings taken for some general computer experience.

Efficiency : decide definition of expertise, get sample expert users (which tends to be difficult), measure time taken to perform typical tasks.

Memorability : get sample casual users (who are usually away from system for certain time/duration) and measure time to perform typical tasks.

Errors : count minor and catastrophic errors made by users while performing some specified task.

Satisfaction : ask users subjective opinion (questionnaire, interview), after trying system for real task.

USABILITY ENGINEERING

The term usability engineering describes a process of user interface development, sometimes referred to as user centred design.
It is a lifecycle process that puts an early emphasis on user and task analysis and actual user involvement in the design and testing of a product.
A product developed with such a user centred process is likely to be a more usable product than one that is developed independent of user considerations and involvement.

USABILITY ENGINEERING LIFECYCLE



Identify user requirements and problems
-Profile Users
-Task Analysis
Identify usability goals based on user requirements
Checkout similar products
Design and prototype a solution (involve users)
Evaluate prototype
-Usability testing (real users and real tasks)
Reiterate steps 4-5 …until users are satisfied

Identify user requirements and problems:

Define your user population.
Determine the distribution of skills, knowledge and experience within your user population.
Assess the user’s skill level with respect to both the task and computer domain.


Identify user requirements and problems:

Typical Profile:
-40 % Novice Users
-57 % Knowledgeable/Intermittent Users
-3 % Expert Users
Other Important Information:
-10 % of user population colour blind
-15 % are the elderly

Identify user requirements and problems:

Task analysis allows a designer to identify the goals and purposes of the intended user group.
This used to involve further analysis of user requirements or investigation/observation of customers
Used to guide user interface design

Identify usability goals based:
Learnability, Efficiency, Memorability, Error, Subjective Satisfaction
Decide in advance on usability metrics and desired level of measured usability
E.g.


Check out similar products (Competitive Analysis):

Competitive analysis of software components
Competitive analysis of competing systems

Parallel Design (Explore design alternatives):
designers should work independently, then compare draft designs

Participatory Design:
Have access to pool of representative users.
Guided discussion of prototypes, paper mock-ups, screen designs with representative users.

Applying Guidelines:
Guidelines . . . general principles and advice about usability characteristics of interfaces
Can be intimidating – often hundreds or thousands of specific recommendations.

Prototyping & Testing:
Perform usability evaluation as early as possible in the design cycle by building and evaluating prototypes