In my experience, the methods described in this book yield consistently good results when applied by skilled practitioners. However, it's unlikely for even the best designer to be exactly right about everything. Collaboration with other designers, design reviews with a team lead, and reviews with engineers, subject matter experts, and stakeholders provide a form of ongoing design evaluation throughout any project. However, it's a good idea to do a more formal type of evaluation at least once before you send your product out into the world. Think of this as the designer's equivalent of QA.
One chapter isn't enough to do any evaluation method justice; my intentions here are merely to introduce the topic, to demonstrate how design evaluation and common evaluation methods fit within the context of Goal-Directed Design, and to help you avoid a few of the most common pitfalls.
When and how you evaluate your design depends on why you're evaluating it. Design evaluation can serve several purposes:
Persuading people there's a problem. If you're the only one who's convinced the existing product or design direction needs work, an evaluation can be an effective tool for changing minds.
Improving design. Some types of design evaluation can help you see if you've designed the right product, while others can help you see if you've designed ...