Plan Do Study Act Cycle of Continual Improvement, also known as the Deming Cycle. The cycle of scientific experimentation used in pursuit of continuous improvement. First introduced by W. A. Shewhart in “Statistical method from the viewpoint of Quality Control” in 1939, originally introduced as a linear sequence of 3 steps and subsequently evolved into the 4step cycle by Shewhart. Shewhart was one of Deming’s mentors, and introduced him to the cycle. Deming built on Shewhart’s concept emphasizing the interactions between the four steps and popularizing the cycle in the area of Total Quality Management.