The statistical thinking underlying Six Sigma is based on the following three principles:All work activities can be done accurately most of the time, empowered employees are necessary for effective control, and good statistical data is an empowered employee's best control tool.All work is a statistically controllable process; 100% control is possible; and every well-controlled process is defect-free.(1) all work is a statistically controllable process; (2) no well-controlled process allows variability; and (3) defect-free work requires tight statistical controls.All work is subject to varying performance outcomes, the amount of variability can be reduced with proper use of statistical methods and controls, and variability declines as tighter and tighter statistical controls are applied.All work is a process, all processes have variability, and all processes create data that explains variability.