statistical process control

Statistical process control (SPC) is a method used to monitor and maintain the quality of ongoing processes, such as manufacturing. It employs statistical methods and graphical displays called control charts to identify variations in output. These variations can stem from common causes (random) or assignable causes (out-of-the-ordinary). When assignable causes are detected, the process can be adjusted to ensure acceptable quality levels.12

Control charts, like the x̄-chart for sample means or p-charts for defect proportions, are constructed with upper and lower control limits, typically set at three standard deviations from the process mean. If a sample's data falls within these limits, the process is considered in control. Data falling outside the limits signals a need for corrective action.12