HUMAN-COMPUTER INTERACTION SECOND EDITION
Dix, Finlay, Abowd and Beale

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Chapter 10 Implementation support Exercises Page 403

10.1 In contrasting the read--evaluation loop and the notification-based paradigm for interactive programs, construction of a pre-emptive dialog was discussed. How would a programmer describe a pre-emptive dialog by purely graphical means? (Hint: Refer to the discussion in Section 10.5 concerning the shift from external and independent dialog management to presentation control of the dialog.)

Chapter 11 Evaluation techniques Page 405

11

Evaluation techniques

Chapter 11 Evaluation techniques Overview Page 405

Evaluation tests the usability and functionality of an interactive system.

Chapter 11 Evaluation techniques Overview Page 405

q Evaluation may take place

-- in the laboratory

-- in the field

Chapter 11 Evaluation techniques Overview Page 405

An evaluation method must be chosen carefully and must be suitable for the job.

Chapter 11 Evaluation techniques 11.1 What is evaluation? Page 406

11.1 What is evaluation?

Chapter 11 Evaluation techniques 11.1 What is evaluation? Page 406

In previous chapters we have discussed methodologies and models which support the design of usable interactive systems. However, even if such techniques are employed, we still need to assess our designs and test our systems to ensure that they actually behave as we expect and meet the requirements of the user. This is the role of evaluation.

Chapter 11 Evaluation techniques 11.1 What is evaluation? Page 406

Evaluation should not be thought of as a single phase in the design process (still less as an activity tacked on the end of the process if time permits). Ideally, evaluation should occur throughout the design life cycle, with the results of the evaluation feeding back into modifications to the design. Clearly it is not usually possible to perform extensive experimental testing continuously throughout the design, but analytic and informal techniques can and should be used. In this respect there is a close link between evaluation and the modelling and prototyping techniques we have already discussed -- such techniques help to ensure that the design is assessed continually. This has the advantage that problems can be ironed out before considerable effort and resources have been expended on the implementation itself: it is much easier to change a design in the early stages of development than in the later stages. We can make a broad distinction between evaluation of the design of an interactive system and evaluation of an implementation, whether full or prototype. The former tends to focus on evaluation by the designer without direct involvement by users; the latter studies actual use of the system. We will discuss evaluation techniques under these two headings. However, it should be noted that these distinctions are not fixed and some techniques can be applied at either stage. Indeed, some techniques have wider application still, being used, as we have seen in Chapter 7, to develop task analyses.

Chapter 11 Evaluation techniques 11.2 Goals of evaluation Page 406

11.2 Goals of evaluation

Chapter 11 Evaluation techniques 11.2 Goals of evaluation Page 406

Evaluation has three main goals: to assess the extent of the system's functionality, to assess the effect of the interface on the user, and to identify any specific problems with the system. The system's functionality is important in that it must accord with the user's task requirements. In other words, the design of the system should enable the user to perform the required tasks more easily. This includes not only making the appropriate functionality available within the system, but making it clearly reachable by the user in terms of the actions that the user needs to take to perform the task. It also involves matching the use of the system to the user's expectations of the task. For example, if a filing clerk is used to retrieving a customer's file by the postal address, the same capability (at least) should be provided in the computerized file system. Evaluation at this level may also include measuring the user's performance with the system, to assess the effectiveness of the system in supporting the task.

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