You're being asked to quantify usability improvements with statistics. But even with a background in statistics, you are hesitant to statistically analyze the data, as you may be unsure about which statistical tests to use and have trouble defending the use of the small test sample sizes associated with usability studies. The book is about providing a practical guide on how to use statistics to solve common quantitative problems arising in user research. It addresses common questions you face every day such as: Is the current product more usable than our competition? Can we be sure at least 70 per cent of users can complete the task on the 1st attempt? How long will it take users to purchase products on the website? This book shows you which test to use, and how provide a foundation for both the statistical theory and best practices in applying them. The authors draw on decades of statistical literature from Human Factors, Industrial Engineering and Psychology, as well as their own published research to provide the best solutions. They provide both concrete solutions (excel formula, links to their own web-calculators) along with an engaging discussion about the statistical reasons for why the tests work, and how to effectively communicate the results. It provides practical guidance on solving usability testing problems with statistics for any project, including those using Six Sigma practices. It shows practitioners which test to use, why they work, best practices in application, along with easy-to-use excel formulas and web-calculators for analyzing data. It recommends ways for practitioners to communicate results to stakeholders in plain English.