Supply Chain Concepts

statistical process control (SPC)

Major Topic Area: quality concepts

Process control, or SPC techniques use statistical theory to determine if a process is in a state of statistical control.

Statistical control is defined by the absence of assignable cause variation.

When a process is in this state the only variation is caused by naturally occurring or normal cause variation.

The following table summarizes the difference between the two causes of variation.

Characteristic	Assignable	Normal
alternative name	special	common
presence	sporadic	always present
cumulative impact	large	small