Metrics & analysisStatistical Process Control

What is SPC?

SPC (Statistical Process Control) monitors a process with control charts that distinguish natural variation (always present) from special variation (which has an identifiable cause). Reaction is required only for special variation — adjusting for natural variation makes the process worse.

The control chart’s limits are calculated from the process’s own history — they are not tolerance limits. A process can be in statistical control and still produce out of spec (stable but incapable), or within spec but out of control (unpredictable).

SPC’s behavioural point is at least as important as the mathematics: it teaches the organisation to react to signals rather than noise.

Related concepts

Six Sigma

Six Sigma is a data-driven improvement methodology that reduces variation and defects in processes. The name refers to the goal of a maximum of 3.4 defects per million opportunities — six standard deviations between the process mean and the nearest tolerance limit.

DMAIC

DMAIC is Six Sigma’s project model in five phases: Define (bound the problem), Measure (measure current performance), Analyze (find root causes with data), Improve (implement and verify solutions) and Control (sustain the gain with management).

Quality at the source

Quality at the source is the principle that errors should be detected and stopped where they arise — by the process and the employee that create them — instead of being caught by inspection further down the chain. No defect is passed on.

From concept to practice

The methods only work when they are anchored in daily routines and leadership behaviour. The operations check shows in 4 minutes where your operations stand — and what the next step is.

Take the operations check