The Concept of Software Usability

The concept of usability• The concept of usability has been defined in multiple ways, usually on one

of the following bases:• Semantics:

– in this case usability is equated to terms such as 'ease of use' or 'user-friendliness', without formal definition of the properties of the construct.

• Features: – here, usability is equated to the presence or absence of certain

features in the user interface such as Windows, Icons, Menus or Pointing devices.

• Operations: – where the term is defined in terms of performance and affective levels

manifest by users for certain task and environmental scenarios.

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Models of Usability• Shackel’s Model of Usability

– Effectiveness• Better than some required level of performance• Range of usage requirements

– Learnability• Within some specified time from installation and start of user

training• Based on some specified amount of training and user support

– Flexibility• Allowing adaptation to some specified percentage variation in task

– Attitude• Within acceptable levels of human cost in terms of tiredness,

discomfort, frustration and personal effort

UsableUser

Interface

Subjective satisfaction

Easiness to learn

Efficiency/ running speed

Low Fatigability

Small number of errors when working

Usability Engineering by Jakob Nielsen (1993)

Usability Attributes– Usefulness– Efficiency– Effectiveness– Learnability– Satisfaction– Accessibility

• Usefulness – the degree to which a product enables a user to achieve his or her goals,

• Efficiency – Quickness with which the user’s goal can be accomplished accurately and completely (usually it is a measure of time)

• Effectiveness – refers to the extent to which the product behaves in the way that users expect it to and the ease with which users can use it to do what they intend

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• Learnability – has to do with the user’s ability to operate the system to some defined level of competence after some predetermined amount and period of training

• Satisfaction – refers to the user perceptions, feelings and opinions of the product

• Accessibility – what makes products (SW) usable by people who have disabilities

(bright light, not enough light, injury, etc.)

April 18, 2023

More justification for usability studies …..

• User interface components can help us understand what they are intended for if they are well designed.

• We need to identify limitations of the user interface and come up with recommendations for improvement

• An interface is useable if it is appropriate for the users and for the task being performed

• Useable systems do not emerge by accident. They are the result of a careful process called usability engineering

• We can not ignore usability when building software products.– There is substantial evidence that attention to usability dramatically

decreases costs and increases productivity

Use Case Modelling • One of the most widely used software engineering techniques

to specify user requirements

• Helps to specify – detailed requirements– sequence of actions, including alternatives of the

sequence– the starting point for usability integration into the

software process

• Usability is not directly considered but it is use-case driven

• We can augment use cases for user interface prototyping

Usability engineering • The term usability engineering refers to concepts and

techniques for planning, achieving and verifying objectives for Software usability.– Is part of managing software development.– Is created with a view that software development is more

than writing a code– It is part of an activity of creating software– It is a process guided by systematic methods and

techniques– Relates to measurable usability goals that must be defined

early in software development– A discipline with roots in several other basic disciplines,

including cognitive psychology, experimental psychology, ethnography and software engineering.

– Purpose, goals and objectives of usability testing• To understand whether users can use the software

equally well• To identify problems• To assess the overall effectiveness of the software • To initiate a repeatable usability study protocol• To resolve problems, to determine exact nature of the

problem• To assess user satisfaction• To improve user experience

– Research questions• Is the current software usable? • Is the software ready for release?• How easily and successfully do users find the

information they are looking for?• How easily can users return to the various options?• Can users perform common tasks within established

bench marks?

• Some examples of Usability Testing– Assessment Test of two prototypes

• Which of the two interface styles are effective?• What are the problems for the user?• For which tasks will users need help further

instructions, or supporting documentation?

Examples …. Cont’d• What type of written information will be

required– Prerequisite, theoretical, procedural, examples,

training

• We can give design interfaces for • Left navigation interface (Design 1)• Top navigation interface (Design 2)

Examples:The system works as intended by theprogrammer, but the user:

P1. Cannot figure out how to start the search. Finally finds out to use F10.

P2. Believes he has completed the task, but forgot to push Update.

P3. Sees the discount code field, but cannot figure out which code to use.

P4. Says it is crazy to use six screens to fill in ten fields.

P5. Wants to print a list of discount codes, but the system cannot do it.

Usability problems

Severity classes:1 Missing functionality

2 Task failure

3 Annoying

4 Medium problem (succeeds after long time)

5 Minor problem (succeeds after short time)

Critical problem =Missing functionality, task failure, or annoying

Purpose:Find usability problems

Fig 1.4 Usability test - think aloud

UserPerforms tasksThinks aloud

LogkeeperListensRecords problems

FacilitatorListensAsks as needed

I try this because ...

User doesn’tnotice ...

Users: 20 bank customers ...

Measure: In 2 min?

Reqs: Task 1: 18 succeed.Task 2: 12 succeed.

Choosing the numbers

Why 20?Cost versus reliability.During development:One, later two, later ...

Why 2 mins?Best practice,ideal way ...

Why 18?90% of customersshould succeed.Task 2 harder.

Open target

Reqs: 18 out of 20 mustsucceed within ____ min.We expect around 2 min.

Specify how, what, and expectations.Wait and see what ispossible.

ATMUsers: 20 bank customers, random selection.Task 1: Withdraw $100 from ATM. No instructions.Measure: How many succeed in 2 min?

Task 2: Withdraw as much as possible ($174)Measure: How many succeed in 5 min?Reqs: Task 1: 18 succeed.

Task 2: 12 succeed.

How to measure

What to measure

Requirement - target

Measuring usability - task time (performance)

Internal ordering systemUsers: 5 secretaries in the company.

Have tried the internal ordering system.Have not used it for a month.

Task 1: Order two boxes of letter paper + . . .Measure: Average time per user.Reqs: Average time below 5 min.

Users: 3 potential users. Think-aloud test. Record usability problems.

Task 1: Order two boxes of letter paper + . . .Task 2: . . .

Measure: Number of critical problems per user.Number of medium problems on list.

Reqs: Max one user encounters critical problems.Max 5 medium problems on the list.

What to measure

Requirement

Fig 1.6C Measuring usability - Problem counts

How to measure

Task 1: Withdraw a standard amount from ATM.Task 2: . . .

Measure: Number of keystrokes and mouse clicks.

Reqs: Max keystrokes 6 - incl. PIN code.Total system response time max 8 s.

How tomeasure

What to measure

Requirement

Fig 1.6D Measuring usability - Keystroke counts

Total task time6 keystrokes @ 0.6 s 3.6 stotal system response time 8.0 sTotal task time 11.6 s

Plus otheruser actions?

Ask 20 novice users to complete the questionnaire.

Measure: Count number of entries per box.

Reqs: 80% find system easy to learn.50% will recommend it to others.

How to measure

What to measure

Requirement

Fig 1.6E Measuring usability - Opinion poll

Questionnaire agree neutral disagreeThe system was easy to learnThe system is easy to useThe system helps me . . .It is fun to useI will recommend it to others

Ask 5 potential ATM users what these error messages mean:

Amount too largePIN code invalid . . .

Ask them also:What would the system do if . . .

Measure: Assess answers on scale A-D.

Reqs: 80% of answers marked A or B.

How to measure

What to measure

Requirement

Fig 1.6F Measuring usability - Score for understanding

Pros: Easy way to test understandability.Best way to cover error messages. Useful both early and late in development.

Cons: Only measures understandability..

Fig 2.1 The development process

Analysis

Operation

Design

Program

Test

Experts?Guidelines?

Usability test?Scaring results !Too late to correct

Traditional systemsdevelopment

Design prototype

ProgramUsability test

Study usersand tasks

Analysis HCI classic:iterative design

Fig 2.3B Defect list for hotel system mockupID Defects in Find Guest/Stay window Novice B Novice M Receptionist D1 The Stay concept is not understood by

ordinary users Medium problem

Guesses immediately

D2 Doesn't notice the Find button Task failure

Medium problem.

D3 When you select a certain date, why does the list show earlier dates too?

Minor problem

D4 Not visible whether the guests have been checked in or not

Annoying

D5 How do you open the stay window from the Find guest/stay window?

Medium problem

Task failure

Medium problem

D6 Tries Enter to search, but it opens a Stay window. Then tries F2

Medium

D7 Doesn't see that the guest is on the list already.

Annoying Annoying

D8 Doesn't understand why the list becomes empty (made a spelling error)

Medium problem

D9 Believes the task is complete when she sees the guest on the list.

Task failure

D10 Doesn't understand that the Stay screen must be opened.

Task failure Task failure

D11 Fills in all search criteria, believing they are data fields.

Minor problem

Task failure

• See examples of bad screen from HCIbook4 on the CD.

Paper Prototypes• Next two slides to be done in groups for class

discussion

Hotel Reservation system

Task listT1. Book roomT2. Check inT3 Check outT4 Change roomT5 Record services and

breakfast list

Data modelD1. GuestsD2. RoomsD3. ServicesBusiness goals:

- Small hotel market - Much easier to useRequirements:R1: Store data according to data model.R2: Support tasks T1 to T5.. . .R7: Usable with 10 minutes of instruction/

orientation.

Video Rental System

Task listT1. Enter Borrower infoT2. Enter Video infoT3. Check out videoT4 Check in video

Data modelD1. BorrowerD2. VideoD3. Services

Business goals: - Much easier to look for films - Much easier to register borrower info

and the film he/she has borrowed

Requirements:R1: Store data according to data model.R2: Support tasks T1 to T4.. . .R7: Usable with 10 minutes of instruction/

orientation.

Summary• Usability studies are carried out to find out

What is working well or poorlyWhat parts of the system need attention?How close are developers to meet overall usability objectives?

Summary …cont’d

Strength of usability engineering• Establishing an agreed upon definition for usability• Setting this difference in terms of metrics and goals

for usability• Putting usability on a par with other engineering goals• Providing a context for discussion of usability• Providing a method for prioritizing usability problems

Summary …cont’d• Usability engineering activities

Development of requirement scenariosDevelopment of basic level task scenariosReview with team membersDevelopment of paper prototypesDevelopment of running prototypes