User Interface Design and Ergonomics - National Open University of ...

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you use. But then you need some way to compare the numbers you get for one design with the numbers from the others. The simplest approach to use is called a BETWEEN-GROUPS EXPERIMENT. You use two groups of test users, one of which uses version A of the system and the other version B. What you want to know is whether the typical value for version A is likely to differ from the typical value for version B, and by how much. Here's a cookbook procedure for this. Using parts of the cookbook method above, compute the means for the two groups separately. Also compute their standard deviations. Call the results ma, mb, sa, sb. You'll also need to have na and nb, the number of test users in each group (usually you'll try to make these the same, but they don't have to be.) Combine sa and sb to get an estimate of how variable the whole scene is, by computing s = sqrt( ( na*(sa**2) + nb*(sb**2) ) / (na + nb - 2) ) ("*" represents multiplication; "sa**2" means "sa squared"). Compute a combined standard error: se = s * sqrt(1/na + 1/nb) Your range of typical values for the difference between version A and version B is now: ma - mb plus-or-minus 2*se Another approach you might consider is a WITHIN-GROUPS EXPERIMENT. Here you use only one group of test users and you get each of them to use both versions of the system. This brings with it some headaches. You obviously can't use the same tasks for the two versions, since doing a task the second time would be different from doing it the first time, and you have to worry about who uses which system first, because there might be some advantage or disadvantage in being the system someone tries first. There are ways around these problems, but they aren't simple. They work best for very simple tasks about which there are not much to learn. You might want to use this approach if you were comparing two low-level interaction techniques, for example. You can learn more about the within-groups approach from any standard text on experimental psychology. 3.1.7 DETAILS OF SETTING UP A USABILITY STUDY The description of user testing given up to this point should be all the background you need during the early phases of a task-centered design project. When you are actually ready to evaluate a version of the design with users, you will have to consider some of the finer details of setting up and running the tests. This section, which you may want to skip on the first reading of the chapter, will help with many of those details. 186
a. Choosing the Order of Test Tasks Usually you want test users to do more than one task. This means they have to do them in some order. Should everyone do them in the same order, or should you scramble them, or what? Our advice is to choose one sensible order, starting with some simpler things and working up to some more complex ones, and stay with that. This means that the tasks that come later will have the benefit of practice on the earlier one, or some penalty from test users getting tired, so you can't compare the difficulty of tasks using the results of a test like this. But usually that is not what you are trying to do. b. Training Test Users Should test users hit your system cold or should you teach them about it first? The answer to this depends on what you are trying to find out, and the way your system will be used in real life. If real users will hit your system cold, as is often the case, you should have them do this in the test. If you really believe users will be pre-trained, then train them before your test. If possible, use the real training materials to do this: you may as well learn something about how well or poorly it works as part of your study. c. The Pilot Study You should always do a pilot study as part of any usability test. A pilot study is like a dress rehearsal for a play: you run through everything you plan to do in the real study and see what needs to be fixed. Do this twice, once with colleagues, to get out the biggest bugs, and then with some real test users. You'll find out whether your policies on giving assistance are really workable and whether your instructions are adequately clear. A pilot study will help you keep down variability in a bottom-line study, but it will avoid trouble in a thinking-aloud study too. Don't try to do without! d. What If Someone Does not Complete a Task? If you are collecting bottom-line numbers, one problem you will very probably encounter is that not everybody completes their assigned task or tasks within the available time, or without help from you. What do you do? There is no complete remedy for the problem. A reasonable approach is to assign some very large time, and some very large number of errors, as the "results" for these people. Then take the results of your analysis with an even bigger grain of salt than usual. e. Keeping Variability Down As we've seen, your ability to make good estimates based on bottom-line test results depends on the results not being too variable. There are things you can do to help, though these may also make your test less realistic and hence a less good guide to what will happen with your design in real life. Differences among test users is one source of variable results: if test users differ a lot in how much they know about the task or about the system you can expect their time and error scores to be quite different. You can try to 187
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] NATIONAL OPEN UNIVERSITY OF NIGER
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National Open University of Nigeria
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Summary ...........................
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UNIT 3 - GRAPHICAL USER INTERFACE (
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Assignments File Tutor-Marked Assig
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2 DESIGN and DESIGNING GOOD USER IN
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need both the study unit you are wo
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CIT 711: USER INTERFACE DESIGN AND
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UNIT 1 FUNDAMENTALS OF USER INTERFA
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3.3 TYPES OF USER INTERFACES Curren
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3.5 USER INTERFACE MODALITIES AND M
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Table of Contents 1.0 Introduction
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3.1.1 DESIGNING A GOOD USER INTERFA
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widgets properly is to read and und
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Figure 1:- Showing that alignment o
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6.0 TUTOR MARKED ASSIGNMENT a. How
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A graphical user interface is a typ
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Operating System. It is easy for a
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A list of items from which to selec
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collaborative work. For example, sc
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MODULE 1 UNIT 4 HUMAN COMPUTER INTE
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3.3 DIFFERNCES WITH RELATED FIELDS
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window blinds to automobile braking
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Wickens, Christopher D., John D. Le
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The International Ergonomics Associ
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approach, the Gilbreths reduced the
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3.6 BENEFITS OF ERGONOMICS The thre
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Another key to reducing lumbar disc
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MODULE 2 - USER INTERFACE DESIGN TE
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methods include inspection methods,
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Determine time of each operation (b
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unable to understand new informatio
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M cones, or, misleadingly, green co
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Motor skill which is a learned seri
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MODULE 2 UNIT 2 UNDERSTANDING USERS
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The users of a system must be ident
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This example brings up an important
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whether you want to have a palette
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Task analysis which includes identi
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MODULE 2 UNIT 3 USER CENTERED DESIG
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or small body text is also hard to
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Introduction to User-centered desig
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organizations themselves. Interacti
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After thorough analysis using vario
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Interaction design which is the dis
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In human-computer interaction and c
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The preferred method for ensuring u
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3.4 ISO STANDARDS FOR USABILITY ISO
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In this unit, you have been introdu
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affect the way the command is execu
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• Guides the user via the predefi
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The term direct manipulation was in
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There are two important reasons for
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UNIT 1 PROTOTYPING Table of Content
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Figure 12: The iterative steps of p
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select print Figure 13: An interfac
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Ambler, S.W. & Constantine, L.L. (2
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3.2 LOW-FIDELITY PROTOTYPES Low-fid
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Figure 14:- Example of Sketching II
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Much more important for features th
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DENIM, an extension of SILK, is a t
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• Encourage menu & forms style, r
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Another problem is that native widg
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interfaces, so that a realistic sim
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UNIT 3 INPUT AND OUTPUT MODELS Tabl
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Recall that perceptual fusion means
Page 136 and 137: 3.2 OUTPUT MODEL There are basicall
Page 138 and 139: directly-mapped pixel image will no
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Page 142 and 143: UNIT 4 MODEL VIEW-CONTROLLER (MVC)
Page 144 and 145: 3.3.2 AS A DESIGN PATTERN MVC enco
Page 146 and 147: The Views are XForms controls for s
Page 148 and 149: UNIT 5 LAYOUTS AND CONSTRAINTS Tabl
Page 150 and 151: 3.5 CONSTRAINTS Constraints are rel
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Page 154 and 155: MODULE 4 UNIT 1 TECHNIQUES FOR EVAL
Page 156 and 157: a. Card Sorting Card sorting is a w
Page 158 and 159: Rapid prototyping is a method used
Page 160 and 161: 3.2.1 THE USE OF PROTOTYPES It is o
Page 162 and 163: Dumas, J.S. and Redish, J.C. (1999)
Page 164 and 165: the users' respect for you as a pro
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Page 168 and 169: speed whenever the average load was
Page 170 and 171: Table 4:- Table: Average times for
Page 172 and 173: phases: list the actions, and then
Page 174 and 175: Nielsen and Molich used their own e
Page 176 and 177: 7.0 REFERENCES AND FURTHER READING
Page 178 and 179: users. If you do not, you can be ba
Page 180 and 181: If you are led to develop more and
Page 182 and 183: It's very easy to shape the comment
Page 184 and 185: a. Analyzing the Bottom-Line Number
Page 188 and 189: ecruit test users with more similar
Page 190 and 191: MODULE 4 UNIT 4 OTHER EVALUATION IS
Page 192 and 193: 3.2 CURRENT ISSUES CONCERNING EVALU
Page 194 and 195: 2.0 OBJECTIVES By the end this unit
Page 196 and 197: It provides a real focal point for
Page 198 and 199: 3.3.4 CONDUCTING THE TEST Having co
Page 200: The stages involved in usability te
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