Ishikawa 1985，第198–199頁: "I divide statistical methods into the following three categories according to their level of difficulty. 1. Elementary Statistical Method (the so-called Seven Tools) ... 2. Intermediate Statistical Method ... 3. Advanced Statistical Method (using computers concurrently)". Ishikawa, Kaoru. What Is Total Quality Control? The Japanese Way. 由Lu, David J.翻译 1st. Englewood Cliffs, New Jersey: Prentice-Hall. 1985. ISBN 978-0-13-952433-2.
