|
Task-Centered User Interface Design
A Practical Introduction |
|
by
Clayton Lewis
and
John Rieman
Copyright ©1993, 1994: Please see the "shareware notice" at the front of the book. |
| Contents | | Foreword | | ProcessUsers&Tasks | | Design | | Inspections | | User-testing | | Tools | | Documentation | |
Chapter 4: Evaluating the Design Without Users
Throughout this book we've emphasized the importance of bringing users into the interface design process. However, as a designer you'll also need to evaluate the evolving design when no users are present. Users' time is almost never a free or unlimited resource. Most users have their own work to do, and they're able to devote only limited time to your project. When users do take time to look at your design, it should be as free as possible of problems. This is a courtesy to the users, who shouldn't have to waste time on trivial bugs that you could have caught earlier. It also helps build the users' respect for you as a professional, making it more likely that they will give the design effort serious attention.
A second reason for evaluating a design without users is that a good evaluation can catch problems that an evaluation with only a few users may not reveal. The numbers tell the story here: An interface designed for a popular personal computer might be used by thousands of people, but it may be tested with only a few dozen users before beta release. Every user will have a slightly different set of problems, and the testing won't uncover problems that the few users tested don't have. It also won't uncover problems that users might have after they get more experience. An evaluation without users won't uncover all the problems either. But doing both kinds of evaluation significantly improves the chances of success.
In this chapter we describe three approaches to evaluating an interface in the absence of users. The first approach is the cognitive walkthrough, a task-oriented technique that fits especially well in the context of task-centered design. The second approach is action analysis, which allows a designer to predict the time that an expert user would need to perform a task, and which forces the designer to take a detailed look at the interface. The third approach is heuristic evaluation, a kind of check-list approach that catches a wide variety of problems but requires several evaluators who have some knowledge of usability problems.
We'll describe these techniques and show how each one applies to the analysis of a single interface. The interface we'll look at is the "Chooser" in an early version of the Apple Macintosh operating system. The Chooser lets the user select printers and printer options. For our task-oriented evaluations, the task will be to turn on background printing.
The Chooser is an interesting example because it's part of a system that was designed with usability and simplicity as paramount goals. Nonetheless, we'll see that it has some potential problems. Some of those problems have been corrected in later versions of the Mac operating system; others haven't, possibly because the structure of the interface is too deeply embedded in the functionality of the system, or possibly because the changes would be too disruptive to existing users. (See the end of Appendix M for more thoughts on upgrading systems after they are in the field.)
Take a few minutes before you read the rest of this chapter to look over the following description of the Chooser and write down any problems you find.
We've presented this example in the rough format that a system designer might use to describe a suggested system to his colleagues. This is the point in an interface design when you should be using the techniques described in this chapter, either alone or as a group -- don't wait until after the system is implemented!
START
User is working with word processor. Task is to turn on background printing. Screen shows the current application window and the following menubar of pulldown menus:
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@ File Edit Search Font Utilities
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("@" stands for the apple icon.)
ACTION 1: Pull down the apple menu.
Apple pulldown menu looks like this:
| @ |
------------------
| About UltraWord |
| ---------------- |
| Alarm Clock |
| Calculator |
| Chooser |
| Control Panel |
| Find File |
| Keycaps |
| Scrapbook |
------------------
ACTION 2: Select "Chooser" from the menu.
A dialog box appears:
---------------------------------------------------
| [ ] |
---------------------------------------------------
| |
| -------------------- ---------------------- |
| | [laser printer |^| | | |
| | icon] |-| | | |
| | | | | | |
| | [dot matrix | | | | |
| | printer icon] |-| | | |
| | |v| | | |
| -------------------- ---------------------- |
| |
| |
| User name: |
| -------------------- |
| | Sneezy | |
| -------------------- |
| Appletalk: |
| o active * inactive |
---------------------------------------------------
ACTION 3: Click on current printer type, which is Laser.
The laser printer icon highlights and new things appear in the dialog box:
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| [ ] |
---------------------------------------------------
| Select a laser printer: |
| -------------------- ---------------------- |
| | [LASER PRINTER |^| | Hotshot | |
| | ICON (high- |-| | Mary's | |
| | lighted)] | | | Last Chance | |
| | | | | | |
| | [dot matrix |-| | | |
| | printer icon] |v| | | |
| -------------------- ---------------------- |
| Background printing |
| o On * Off |
| User name: |
| -------------------- |
| | Sneezy | |
| -------------------- |
| Appletalk: |
| o active * inactive |
---------------------------------------------------
ACTION 4: Click the On button under background printing.
The On button highlights and the Off button unhighlights.
ACTION 5: Click the Close Box in the upper left window.
The screen appears as it did at startup.
| Copyright © 1993,1994 Lewis & Rieman |
| Contents | | Foreword | | ProcessUsers&Tasks | | Design | | Inspections | | User-testing | | Tools | | Documentation | |