15. task models

EXERCISE 15.8 [extra - not in book]

(Cross-refer to Chapter 9) This is a extended design exercise in two parts. The first part uses information from users to develop a design for a mobile phone. The second part uses different evaluation techniques to assess the design.

There are two aims: to demonstrate how the views of users can be incorporated into design and to demonstrate the different information that can be gained by using different evaluation methods.

You have been asked to design a mobile phone taking into account the user views expressed below, determined from market research studies.

There are a number of factors that have to be considered in the design, ranging from the way information is entered into the system and the manner in which it is presented back to the user, through aesthetic judgements to the functionality that the system should offer.

1. Design

Read the user responses given below and then analyze them under the following headings:


You need to determine the tasks that users wish to perform with the phone, and how they want to go about performing those tasks. You need to decide what features your phone should offer and what are dispensable. You are constrained by real-life costs and so will have to trade off size for weight and battery life, cost against functionality, and so on.

Try to identify the real issues that people consider when using a mobile phone. Try to see what factors will influence their decision about which phone to buy. It is these that must motivate your design. Make a list of the features you feel your phone must have.


How are you going to present all this information to the user? What style of output is most suitable? What is the best way to interact with it? Will you present all the information at once? What input characteristics will your phone have: how will numbers be entered, functions accessed, and so on?

Having thought about these things, consider that you are also trying to keep the electronics inside the phone as simple as possible. Remember too that people will not carry a manual for their phone around with them, and so they will need to be able to understand what to do, or to be reminded by the interface itself.


Consider issues of overall colour, size, shape, texture; of button spacing, layout, colour and feedback; display size and placement; information display.

You will use this analysis as the basis of your design. Modelling techniques such as task analysis can help to clarify this, which will in turn make the process of design easier.

Having decided upon all the relevant information, now design your phone. You have to produce two views of the phone.

  • The first is a picture of the phone as it appears to the user, with no additional labelling - make this as high quality as you can. Imagine it is the sort of picture that would appear in a brochure advertising the phone.
  • The second view is of the same phone seen from above.
  • An additional set of pictures of parts of the phone should also be provided that would enable you to run through a typical interaction with a prospective user, showing the display state when they perform certain actions to achieve a certain function.

Either do all of these designs separately on paper, using colour, shading and different viewpoints as appropriate, or utilise OHPs to overlay the basic design. This is particularly useful for the second view of the phone as it allows you to update the display state without requiring redrawing of the rest of the phone.

Again, modelling techniques can help in the development of an effective dialog. Consider, for example, using a dialog notation to describe the details of your interface or performing a GOMS analysis of the main tasks supported by your design.

Mobile Phone: User Responses

A group of people were interviewed to obtain their views on the features they would expect to find in their ideal mobile phone. Some of the people currently use a mobile phone, others do not. Given below are the (edited) texts of their responses.

A. 'I want to keep track of the number of calls that I make, and the cost of the calls. Since I use the phone for business it has to be small but powerful but can't cost a lot to buy. I don't want to fuss with that stupid aerial thing that you have to flip up in order to use it and I want to be able to keep ringing people back if they're busy - as I said it has to be hand-held but that's it really.'

B. 'Ohhh - a mobile phone! Well, it just has to ring people and let people ring you, doesn't it.'

C. 'It must be able to store telephone numbers as I won't have my telephone book with me, but I dunno how I'd search for the numbers - perhaps a pad on which you could write them down would be a good idea - no that's daft really isn't it, I mean it's supposed to be electronic, what about a volume control for ringing? I remember someone's phone going off in a meeting. It was really loud and she was so embarrassed .....what about the buttons, will it have press buttons or a dial? Oh I can decide - well I like the dial personally, I think it's aesthetically pleasing, but some people like buttons. I dunno really. Running them costs a lot of money so I suppose I'd like to be able to tell how much I'd spent that day on calls - sort of get my bill as I go along, I suppose. Will I be able to turn it off? Oh - I have to decide, do I? Well, I suppose I should have it with me and on all the time but what if I didn't want to be interrupted? So I suppose I'd want to turn it off ..... but then I may miss important calls - can I have an answering machine built in as well or something so that it answers my calls if I'm not there - that would be nice.'

D. 'I wouldn't use one ever - yuppie toy!'

E. 'Well, the buttons would have to feel nice as I hate those plasticky tacky ones you get on those cheap phones. It's difficult to tell when the button has been pressed sometimes. Some sort of display would be good - I suppose it should have information on the status of things - battery, maybe, and the signal strength, the number I'm calling, the previous numbers so that I can scroll back and get them, and perhaps an address book thingy that has names and addresses and telephone numbers in. Hmmm, that's a bit bulky, right - I'd want it to be pocket-sized too. Oh, and the batteries should have to last for ages and ages and I want to be able to charge it up anywhere like in the car and so on.'

F. 'Oh - I'd never have one because what if I lost it? It's not the cost of the phone that's the problem, it's that someone may ring up their friend in Australia and I'd have to foot the bill. It would be okay if only I could use it.'

G. 'Wow - mobile phones are great - I want one that rings people up, takes messages, will allow me to send faxes and receive them, will act as a calculator as well - I mean there's all those number buttons already, right? - and an address book and small word processor - it's got to have a display and things, right? so it could also be a personal organiser and interface to PCs and Suns and Macs and things and it must be small; that's for certain, it has to be small and the battery has to last for a week or so without being recharged and handheld - no, I said that - errrm ... that's it. Oh, and I want to use it with the interface bit so as I can read my email on the Suns when I'm away and stuff.'

H. 'Easy: 1. see the number I'm ringing. 2. be able to redial easily when a number is busy. 3. see the battery strength. 4. see how much it's cost me. 5. have nice buttons to press with good feedback. 6. not have to re-enter all a long number if I make a mistake. That's all'

I. I'd like a system that has an address book in it, but it doesn't have to be too powerful. Then I want to be able to see what number I'm ringing and re-ring it if necessary and see how much the calls have cost. A good aerial will be needed because good reception is really important. A way of barring calls to international numbers would be good and a way of barring others from using it would also be nice. I'd want to turn it off occasionally but I dunno what would happen if anyone tried to ring me.'

J. 'I like them, especially the grey ones - they're better than the black - and the pretty light that comes on, that's good too - dunno what it's for though.''

K. 'I don't like them - because I'm a bit deaf they're too quiet for me and I can't hear what people are saying.'

L. 'Ha! what would be nice is a phone with not too many buttons! They all have too many buttons nowadays and I hate that. Keep it simple, I reckon.'

M. 'I don't understand them. I never know which button to press to get the phone to ring and which to press to stop a call, and I can never work out how to answer it either - do you just pick it up or what? And what are the letters on the number buttons for? You know -- the 1 has 'abc' on it and so on?'

N. 'What's a mobile phone - a cordless one? Oh, one of those things. Naw, I don't want one of those - they're like half a housebrick.....oh, I can choose, can I - well, I just want the same as I've got at home - small, you know, but having it portable. That's all I want.'

2. Evaluation

The second part of this exercise concentrates on the evaluation of your design and looks at two different evaluation methods: heuristic evaluation and think aloud.

The first evaluation method is 'heuristic evaluation'. You will evaluate your design against a set of general usability criteria (laid out below):

  • visibility of system status
  • match between system and the real world
  • user control and freedom
  • consistency and standards
  • error prevention
  • recognition rather than recall
  • flexibility and efficiency of use
  • aesthetic and minimalist design
  • help users recognize, diagnose and recover from errors
  • help and documentation

These criteria are discussed in more detail in Section 9.3.2

The aim of the heuristic evaluation is to debug the design; to highlight the points in the design that are inconsistent or likely to cause users problems.

If you can, also exchange designs with a colleague. Evaluate each other's designs using all of the design material and the usability criteria given above. During your evaluation, consider if there are other general criteria that are important considerations for this particular example; if so, include them. You are aiming to see where the design is successful and where it fails; it may assume too much, or too little, it may not offer any feedback, or present an unclear view of what is happening. The user may be expected to remember too many things at once, or there may be different ways to do similar things.

Make notes of your evaluation.

At the end of this stage, you should have done a heuristic evaluation of your design and, if possible, have received an independent evaluation of it. Compare these evaluations, collating similar problems and resolving differences, until you have an accurate summary of the evaluation.

Complement the heuristic evaluation with the observational technique of think aloud. For this you need one or more people to help you.

As an evaluator, spend a few minutes thinking of some scenarios and tasks for the user to perform. For example, to look up a telephone number, to meter a call, or to dial a number. Include some complex tasks as well as some simple ones. Ask the user to step through these tasks using each design, 'thinking aloud' as they do so - describing what they think is happening, why they take an action, what they are trying to do. Take notes on the user's actions, comments and any problems. The fuller the detail in the protocol, the better.

Note to the 'user': Follow the evaluator's instructions. Try to give as much information as possible. People tend to say less when they are unsure what to do, but this is the time that the evaluator needs to know most. Go through explaining which buttons you would press and when, giving the designer the chance to show you what, if anything, would happen to the display.

Look at the results from the heuristic evaluation and the think aloud. Notice where they highlight problems in the design. Also look for instances in which the design allows tasks to be easily accomplished. Compare the two techniques and note anything which is identified by one technique and not the other.


Reappraise your design carefully in the light of the evaluation process. Carefully look at things that cause confusion, at the functions that are there but may never be used, and comments your users made about the good and bad points of your design. Try to come up with a new version of the phone. It should incorporate all the good features of the previous prototype, while avoiding all the problems that it may have suffered. Having decided, produce a final labelled drawing of the ideal phone.

answer available for tutors only

extended project

Other exercises in this chapter

ex.15.1 (ans), ex.15.2 (ans), ex.15.3 (ans), ex.15.4 (ans), ex.15.5 (ans), ex.15.6 (tut), ex.15.7 (open), ex.15.8 (open), ex.15.9 (tut), ex.15.10 (tut), ex.15.11 (tut)

all exercises for this chapter