User Interface Design

Transcription

1 User Interface Design Winter term 2005/2006 Thursdays, c.t., Raum 228 Prof. Dr. Antonio Krüger Institut für Geoinformatik Universität Münster 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 1

2 Testing & modeling users 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 2

3 The aims Describe how to do user testing. Discuss the differences between user testing, usability testing and research experiments. Discuss the role of user testing in usability testing. Discuss how to design simple experiments. Describe GOMS, the keystroke level model, Fitts law and discuss when these techniques are useful. Describe how to do a keystroke level analysis. 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 3

4 Experiments, user testing & usability testing Experiments test hypotheses to discover new knowledge by investigating the relationship between two or more things i.e., variables. User testing is applied experimentation in which developers check that the system being developed is usable by the intended user population for their tasks. Usability testing uses a combination of techniques, including user testing & user satisfaction questionnaires. 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 4

5 User testing is not research User testing Research experiments Aim: improve products Aim: discover knowledge Few participants Many participants Results inform design Results validated statistically Not perfectly replicable Replicable Controlled conditions Strongly controlled conditions Procedure planned Experimental design Results reported to developers Scientific paper reports results to community 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 5

6 User testing Goals & questions focus on how well users perform tasks with the product Comparison of products or prototypes common Major part of usability testing Focus is on time to complete task & number & type of errors Informed by video & interaction logging User satisfaction questionnaires provide data about users opinions 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 6

7 Testing conditions Usability lab or other controlled space Major emphasis on selecting representative users developing representative tasks 5-10 users typically selected Tasks usually last no more than 30 minutes The test conditions should be the same for every participant Informed consent form explains ethical issues 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 7

8 Type of data (Wilson & Wixon, 97) Time to complete a task Time to complete a task after a specified time away from the product Number and type of errors per task Number of errors per unit of time Number of navigations to online help or manuals Number of users making a particular error Number of users completing task successfully 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 8

9 Usability engineering orientation Current level of performance Minimum acceptable level of performance Target level of performance 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 9

10 How many participants is enough for user testing? The number is largely a practical issue Depends on: schedule for testing availability of participants cost of running tests Typical 5-10 participants Some experts argue that testing should continue until no new insights are gained 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 10

11 Experiments Predict the relationship between two or more variables Independent variable is manipulated by the researcher Dependent variable depends on the independent variable Typical experimental designs have one or two independent variable 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 11

12 Experimental designs Different participants - single group of participants is allocated randomly to the experimental conditions Same participants - all participants appear in every condition Matched participants - participants are matched in tuples, e.g., based on expertise, gender 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 12

13 Example Hypotheses: Will the time to read a screen of text be different if 12-point Helvetica is used instead of 12-point Times-Roman? Condition 1: users read text with Helvetica Condition 2: users read text with Times Roman Control condition: read text on paper Extend design with variable user-expertise (additional conditions: expert/beginner) What are the independent and dependent variables 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 13

14 Advantages and disadvantes 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 14

15 Evaluation of results / significance The larger the sample, the less likely that the difference is due to sampling errors or chance. The larger the difference between the two means, the less likely the difference is due to sampling errors The smaller variance among the participants, the less likely that the difference was created by sampling errors. 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 15

16 Variablitiy Are the results statistically significant? Use the t-test to analyze the ration of means and group variability 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 16

17 T-test Use standard-table of significance to determine if t is good enough. From: Februar 06 IfGi Universität Münster User Interface Design A. Krüger 17

18 Predictive models Provide a way of evaluating products or designs without directly involving users Psychological models of users are used to test designs Less expensive than user testing Usefulness limited to systems with predictable tasks - e.g., telephone answering systems, mobiles, etc. Based on expert behavior 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 18

19 GOMS (Card et al., 1983) Goals - the state the user wants to achieve e.g., find a website Operators - the cognitive processes & physical actions performed to attain those goals, e.g., decide which search engine to use Methods - the procedures for accomplishing the goals, e.g., drag mouse over field, type in keywords, press the go button Selection rules - determine which method to select when there is more than one available 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 19

20 Keystroke level model GOMS has also been developed further into a quantitative model - the keystroke level model. This model allows predictions to be made about how long it takes an expert user to perform a task. 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 20

21 Response times for keystroke level operators 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 21

22 Problems of GOMS/Keystroke model Doesn t take into account slack times and critical situations that may slow down certain strokes. Example: Usage of system while talking to a person in parallel. Further influences that are not taken into account: fatigue, learning effects, workload, etc.. Models are just good to provide an estimate, they can t substitute user testing 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 22

23 Fitts Law (Paul Fitts 1954) The law predicts that the time to point at an object using a device is a function of the distance from the target object & the object s size. The further away & the smaller the object, the longer the time to locate it and point. Useful for evaluating systems for which the time to locate an object is important such as handheld devices like mobile phones Why are labeled toolbars easier to access? 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 23

24 Key points User testing is a central part of usability testing Testing is done in controlled conditions User testing is an adapted form of experimentation Experiments aim to test hypotheses by manipulating certain variables while keeping others constant The experimenter controls the independent variable(s) but not the dependent variable(s) There are three types of experimental design: different-participants, sameparticipants, & matched participants GOMS, Keystroke level model, & Fitts Law predict expert, error-free performance Predictive models are used to evaluate systems with predictable tasks such as telephones 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 24

25 Design & evaluation in the real world 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 25

26 The aims Show how design & evaluation are brought together in the development of interactive products. Show how different combinations of design & evaluation methods are used in practice. Describe the various design trade-offs & decisions that have to be made in the real world. 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 26

27 Key issues: From requirements to design which design cycle to use which combination of methods to use when designing & evaluating a product what happens when the product being developed is confidential and there are no users available to test it? how many users should be involved in tests? what to do with the evaluation findings how much to expect from users 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 27

28 Case study: designing mobile communicators Two examples, for very different audiences: Nokia s mobile communicator Philips communicator for children 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 28

29 Designing Nokia s mobile communicator design cycle: iterative user-centered approach which methods: ethnographic research scenarios and task models confidential product issues: first in the market is key evaluation must be very limited and no real users 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 29

30 Designing Nokia s mobile communicator (contd) physical aspects: screen size number of buttons versus functionality consistency issues internal consistency (within mobile software) external consistency (with desktop software) user testing none before release summative testing & questionnaires after 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 30

31 Designing telephones for special user groups (Royal Nation Institute for the Blind) Guarded or recessed keys Sidetone reduction to reduce noise level Adjustable key pressure Audio and tactile feedback Larger key size 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 31

32 Consistency of the Design Internal consistency Nokia style guide External consistency difficulties No pointing device Slow connection and download times Default homepage Transcoding webpages (focus on text) 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 32

33 Philips Communicator for children (Oosterhoolt 96) 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 33

34 Designing Philips communicator for children design cycle: iterative and evolutionary which methods: low-fidelity prototyping participatory design interface metaphors physical aspects: color, shape, size, robustness pen input bags to protect screen 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 34

35 Designing Philips communicator for children user involvement: children involved throughout prototypes evaluated constantly invaluable insights for the designers lessons learned: agree on assumptions in requirements think of follow-on projects early on users are not designers act quick and dirty if necessary 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 35

36 Case study 2: A telephone response information system (TRIS) Interactive voice response systems are common in government offices and large companies. Do you know of examples that you have used? Why are these systems often so frustrating to use? Forming a mental model is difficult because there is no visual feedback and the user must remember the menu structure Many menus and deep menus are particularly difficult 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 36

37 Why was TRIS difficult to use? Having to remember the menu structure. The programmers traded computational elegance for usability, e.g., the system asked for social security number and employee identification number, confusing users who did not have both. TRIS was comprised of different systems each with its own interaction style. Users were not told this but when they moved between the systems they experienced sudden, unexplained changes. 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 37

38 How was TRIS evaluated? A combination of techniques were used: a review of the literature provided information about problems with interactive voice response systems expert reviews GOMS analysis of the proposed redesign The redesign was implemented usability tests confirmed that the redesigned system offered better usability than the original design 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 38

39 Why was using different methods valuable? The evaluators were able to build-up a broad picture of usability problems. Using GOMS and heuristic evaluation they could explore the potential benefits of the redesigned system. User testing enabled them to confirm that the redesigned system offered better usability. User satisfaction questionnaires confirmed that users preferred the redesigned system. 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 39

40 Key points Design involves trade-offs Design space for making changes when upgrading a product is limited Cycles of rapid prototyping and evaluation allow designers to examine alternatives Piecing together evidence from a variety of sources can be valuable 20. Februar 06 IfGi Universität Münster User Interface Design A. Krüger 40