In 1942, Shewhart framed Bell Telephone's problem using which terms?

The choice of "Assignable cause; chance cause" reflects the fundamental concepts of variation that Walter Shewhart introduced in his work on statistical quality control. In the context of these terms, an assignable cause refers to a specific, identifiable source of variation that can be controlled or eliminated, such as a malfunctioning machine or a flawed process. This contrasts with chance cause, which represents the inherent variability in a process that cannot be easily attributed to any particular source; it is the random variation that is expected in any production process.

By framing the problem in these terms, Shewhart emphasized the importance of distinguishing between these two types of variation in order to improve quality and process control. Understanding the difference allows teams to focus their efforts on reducing assignable causes while recognizing that chance causes are a normal and unavoidable aspect of production. This foundational idea set the stage for future developments in quality management methodologies, including Six Sigma.