TYPES OF EVALUATION

Most of this book covers methods for creating usable designs. This chapter, however, focuses on evaluating your designs, measuring how well you've done. To what extent is your design usable, what are the problems with the design, and how can you fix those problems? We'll present three primary approaches: usability inspection, group walkthroughs, and user testing.

Some of the earlier methods (surveys, interviews, focus groups) were introduced as ways to uncover user needs but can also serve as ways to evaluate designs with user feedback. Those techniques work well at capturing users' subjective reactions to designs. We've also covered additional evaluation methods, such as hit logs analysis and gathering user feedback, in Chapter 11. Those methods are ones that gather actual usage data and require a site to be live in order to apply them. This final chapter addresses methods that work well for capturing a number of other usability factors, such as speed, errors, incorrect mental models, and memory limitations.

A usability inspection involves a user interface designer sitting down at a desk and evaluating the user interface of a web site based on general design principles or specific lists of guidelines. A group of designers can inspect the site independently and then combine notes to obtain a comprehensive list of problems with the site.

In a group walkthrough, a group of stakeholders in the design gets together and walks through common tasks on the web site. At each step of the...