Quality Control
Updated 2026-08-11
INTRODUCTION
English translation pending.
CORE DEFINITION
Quality control is the discipline of managing variation inside the production process instead of sorting defects at the end. W. Edwards Deming taught statistical quality control in Japan in 1950, and Japanese manufacturers later became the benchmark for quality. The arithmetic behind it is multiplicative: twenty steps each at 95 percent yield produce only about 36 percent good output, so final inspection can remove defective units but cannot recover the losses already incurred. Control points moved upstream catch deviations before downstream value is added, which is why quality is an outcome of process design.
SCAFFOLDING EFFECT
Reduce cognitive load
- Yield math: multiply the individual step yields to see where the total output actually lands - Control point move: shift inspection further upstream to before any value gets added - Variation hunt: remove the systemic causes of variation instead of blaming individual people
Anchor fast decisions
In a serial process, output is good only if every step succeeds, so total yield is the product of the individual yields and falls faster than any single step degrades. A defect created early is carried through all remaining steps, so its cost grows with each stage that adds value. End-of-line inspection cannot raise the yield because the loss has already happened; it can only detect it. Placing control points earlier removes deviations before downstream effort is spent, and monitoring variation separates systemic causes from random noise.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- mungermodels.comhttps://mungermodels.com/models/quality-controlverified
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