This popular textbook gives a clear and lucid account of the underlying principles of statistical methods. The fourth edition has been revised and updated to reflect the growing popularity of statistics and chemometric methods and new approaches in optimization and experimental design. The authors have also addressed the quality of analytical chemistry data and experimental results, an area of increasing concern to chemists testing the safety of food and medicines. This book will suit undergraduate, M.Sc. and graduate courses in Analytical Chemistry and related topics, and will also be valuable for researchers and chemists working in analytical chemistry everywhere.