CONCEPT
Normalization of Deviance
Diane Vaughan's four-phase institutional process — observation, assessment, normalization, baseline shift — by which anomalies become routine and the standards that would have caught them erode incrementally, invisibly, and without any single decision anyone would recognize as wrong.
The concept, developed in Diane Vaughan's The Challenger Launch Decision (1996), names the structural mechanism through which engineering institutions slide toward catastrophic failure not through dramatic bad decisions but through the accumulation of small accommodations each of which, taken alone, appeared reasonable. O-ring erosion on the Space Shuttle began as an unexpected anomaly. Each subsequent launch in which erosion occurred without catastrophic failure constituted, in institutional terms, evidence that erosion was acceptable. The acceptance narrowed the margin. By January 1986, the margin was zero, and the institution had arrived at that margin through a sequence of locally rational decisions that, aggregated, produced an irrational outcome. Petroski drew on Vaughan's framework to illustrate the dynamics of the complacency cycle at finer temporal resolution: the cycle operates not only across generations but within the career of any given engineer, and the normalization of deviance is the within-career mechanism by which margin erodes.
