Two Sigma: Usability and Six Sigma Quality Assurance (Jakob Nielsen's Alertbox)
In the same vein as Mark Hurst's R.O.S.E. framework, Jakob Nielsen describes how usability can benefit from the Six Sigma methodology. Those who know Six Sigma will recognize the acronym DMAIC. Here is how Jakob describes DMAIC in terms of usability testing:
Six sigma quality engineering relies on a five-step process called DMAIC, which stands for define, measure, analyze, improve, and control. By employing each of these steps, Web projects can move toward better and more systematic quality achievements.
Define. As the very first step, specify which usability attributes your customers value most. Which top tasks must be easy for users to perform? How fast should users be able to accomplish critical goals?
Measure. I usually advocate qualitative usability studies, because usability's main goal is to drive the design. For formal quality assurance, however, you must run quantitative studies to collect hard numbers that show how well or poorly your design scores on the usability criteria you defined above.
Analyze. Most likely, there will be a gap between the measurement results and the level of quality you desire. Analyze the test results to identify the root causes; this not only lets you make specific design changes, but also helps you determine why these usability flaws made it into your design in the first place.
Improve. Fix the design. Removing the flaws is an obvious step, but you should also fix your design process so that you introduce fewer flaws the next time you design something.
Control. Don't slack. You must continue to monitor the quality level of your user experience as you introduce more advanced task support, and as users' expectations for usability increase over time. Improve your design methods and retain accountability for each team member's contribution to overall quality.
The last bullet may be the most important. A key lesson from many other fields is that continuous quality improvement is the way to true excellence. That's a lucky break: Web usability is so far behind that there's no hope of reaching acceptable quality in a single leap. Continuous improvement is our only chance.