Definition of Statistical Process Control (SPC):
Statistical process control is the application of statistical methods to identify and control the special cause of variation in a process
Statistical Process Control (SPC) is the equivalent of a histogram plotted on its side over time. Every new point is statistically compared with previous points as well as with the distribution as a whole in order to assess likely considerations of process control (i.e., control, shifts, and trends). Forms with zones and rules are created and used to simplify plotting, monitoring, and decision making at the operator level.
SPC separates special cause from common cause variation in a process at the confidence level built into the rules being followed (typically 99.73% or 3 sigma).