influencing factors in usability tests

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  • Influencing Factors in Usability Tests

    The testing Situation, the Product Prototype, and the Test User

    Sonderegger Andreas

  • ii

    Dissertation zur Erlangung der Doktorwrde an der Philosophischen Fakultt der Universitt Freiburg (Schweiz). Genehmigt von der Philosophischen Fakultt auf Antrag der Professoren Jrgen Sauer (1. Gutachter) und Andy Tattersall (2. Gutachter). Freiburg, den 2. November 2010 (Datum der Thesenverteidigung). Dekan Prof. Dr. Thomas Austenfeld

  • Thank you Jrgen

    Merci Sora

    Fr Nils

  • CONTENT 1 BACKGROUND AND RATIONALE OF THESIS ........................................................................................ 1 2 USABILITY AND THE EVALUATION OF USABILITY ............................................................................ 3

    2.1 DEFINITION OF THE TERM USABILITY ................................................................................................................ 3 2.2 USER EXPERIENCE ............................................................................................................................................ 4 2.3 USABILITY TESTING IN PRODUCT DEVELOPMENT .............................................................................................. 5 2.4 MEASURES IN USABILITY TESTS ........................................................................................................................ 7

    2.4.1 Performance data ................................................................................................................................... 8 2.4.2 Perceived usability ................................................................................................................................. 8 2.4.3 User emotions and user experience ........................................................................................................ 9 2.4.4 Physiological measures ........................................................................................................................ 10 2.4.5 Usability Problems ............................................................................................................................... 10 2.4.6 Relation between usability measures.................................................................................................... 11

    3 THE FOUR FACTOR FRAMEWORK OF CONTEXTUAL FIDELITY INFLUENCING FACTORS IN USABILITY TESTS ................................................................................................................................... 13

    4 OVERVIEW OF THE FOUR STUDIES PRESENTED IN THIS THESIS ............................................... 17 5 THE INFLUENCE OF LABORATORY SETUP IN USABILITY TESTS: EFFECTS ON USER

    PERFORMANCE, SUBJECTIVE RATINGS AND PHYSIOLOGICAL MEASURES ........................... 21 6 THE INFLUENCE OF DESIGN AESTHETICS IN USABILITY TESTING: EFFECTS ON USER

    PERFORMANCE AND PERCEIVED USABILITY .................................................................................... 41 7 THE INFLUENCE OF PROTOTYPE FIDELITY AND AESTHETICS OF DESIGN IN USABILITY

    TESTS: EFFECTS ON USER BEHAVIOUR, SUBJECTIVE EVALUATION AND EMOTION .......... 59 8 THE INFLUENCE OF CULTURAL BACKGROUND AND PRODUCT VALUE IN USABILITY

    TESTING .......................................................................................................................................................... 77 9 GENERAL DISCUSSION ............................................................................................................................... 79

    9.1 OVERVIEW OF FINDINGS ................................................................................................................................. 79 9.2 INTEGRATION OF FINDINGS ............................................................................................................................. 79 9.3 EFFECT SIZES OF INFLUENCING FACTORS ........................................................................................................ 85 9.4 RELATIONS BETWEEN THE DIFFERENT OUTCOME MEASURES IN USABILITY TESTS .......................................... 88 9.5 IMPLICATIONS FOR THE 4FFCF ...................................................................................................................... 90 9.6 IMPLICATIONS FOR FURTHER RESEARCH ......................................................................................................... 91 9.7 IMPLICATIONS FOR USABILITY PRACTICE ........................................................................................................ 93 9.8 CONCLUSION .................................................................................................................................................. 96

    10 REFERENCES ................................................................................................................................................. 97

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    1 Background and rationale of thesis

    The role technology plays in our life is getting more and more important. It pervades our daily

    life and activities since many of the products we use every day are operated via a more or less

    complex interface; the home stereo system, the coffee machine, the micro wave oven, the DVD-

    recorder, the personal digital assistant (PDA), the computer but also products outside the own

    household such as the ATM machine or the ticket vending machine. Coming along with the

    constantly increasing technological progress, products are being continuously upgraded and

    developed and their inherent features and functions become more complex. Whereas a telephone,

    at its origin, served exclusively as a device allowing two persons to talk to each other over

    distance, modern mobile phones can be used for writing emails, watching videos, listening to

    radio, organizing appointments, playing games, and they even offer the possibility for use as

    camera and GPS-navigation device. The increasing complexity of products and functionalities

    may represent a risk that users might be hindered using them in an efficient, flawless, and

    satisfactory way. For product developers it is hence a particular challenge to design products that

    are easy and comfortable to use.

    To ensure the development of user-friendly products1, it is important to guarantee that the

    needs and limitations of the user are taken into account throughout the whole development

    process (Rubin & Chisnell, 2008). This user-centred approach is widely accepted in product

    design and embodies three main principles of design: a) early focus on users and tasks, b)

    empirical measurement, and c) iterative design (Gould & Lewis, 1985). This implies that

    designers should bear the end user in mind throughout the whole design process. For that

    purpose, the authors propose to include the user very early into the design process. To do so,

    users should use simulations and prototypes of the product to carry out real tasks while their

    performance and reactions to the product should be observed, recorded, and analyzed empirically.

    Based on those empirical findings, the product should be developed further, with the aim to

    create a new prototype which can be tested with users again this iterative process of user testing

    and further development should lead finally to a functional product that corresponds to the

    1 In literature on human-computer interaction, authors use different terms when they refer to the object that should be usable (e.g. interface, system, software or computer). In this thesis, the term product is used, which can include physical objects (e.g. mobile phone) or non-physical designs (layout of a webpage) that have a utilitarian function. In contrast, works of art or non-utilitarian items are excluded from this categorization.

  • 2

    requirements and limitations of the user (Gould & Lewis, 1983). The essential role of usability

    tests in such a user centred design approach indicates the importance of this evaluation method

    for the development of usable products (Lewis, 2006).

    In a usability test, a typical usage scenario is simulated, in order to assess the usability of

    a product. In a typical usability test situation, a test user operates a prototype of a product in a

    laboratory which is especially equipped for this purpose (Rubin & Chisnell, 2008). The

    simulation of the product usage may hence differ considerably from the scenario of its real use:

    observers and a camera are present, the product is simulated by a prototype, and the test user

    might differ from the end user of the product (e.g. with regard to expertise, motivation or

    culture). Such contextual factors may represent an important issue for the validity of usability

    tests, since there is no guarantee that effects detected in such an experimental condition prove to

    be the same in a real life context (Jordan, 1998a). Given the significance of usability testing for

    product development, it is important for usability practitioners to be aware of these issues and to

    know in detail how specific contextual factors of usability tests influence its outcomes.

    Awareness of such influencing factors may provide indications about the adequate interpretation

    of usability test results and may help to plan and conduct the usability evaluation. Until now

    however, only little is known about the influence of contextual factors in usability tests on their

    outcomes.

    This thesis is aimed at in

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