shigeo-shingo's radical argument that quality control as traditionally practiced — inspection of finished products, statistical sampling, acceptable quality levels — is fundamentally misguided. Originally published in Japanese in 1985 as 『源流検査とポカヨケ・システム：不良＝0への挑戦』. English edition: "Zero Quality Control: Source Inspection and the Poka-Yoke System," Productivity Press, 1986.
Overview
Shingo argues for three innovations: (1) source inspection — checking conditions at the point where defects originate rather than after products are completed, (2) poka-yoke devices that prevent errors or detect them immediately, (3) immediate feedback when abnormalities are detected. Together, these achieve "zero defects" not through worker exhortation (the Philip Crosby approach) but through process design.
Key Arguments
The book is deliberately provocative. Shingo argues that statistical quality control, including the methods taught by w-edwards-deming, is a valuable but intermediate step that should be superseded by source inspection and mistake-proofing. His logic: SQC detects variation after it has occurred, while poka-yoke prevents defects at their source.
Shingo provides 112 specific examples of poka-yoke devices developed on the shop floor, most costing less than $100 to implement. His most striking case: in 1977, zero monthly defects were achieved in a 30,000-unit/month washing machine assembly process at the Shizuoka plant of Matsushita Electric — proof that zero defects was not aspirational but operationally achievable.
Significance
The book establishes poka-yoke as a systematic engineering discipline rather than a collection of ad hoc tricks. Its challenge to SQC is significant: where Deming emphasized statistical understanding of variation, Shingo argued for designed-in prevention. Both approaches are now understood as complementary — SPC for system-level monitoring, poka-yoke for point-of-origin prevention.