Levey-Jennings Charts show the relationship of control limits to which distribution type?

• A. Uniform Distribution
• B. Gaussian Distribution
• C. Log-normal Distribution
• D. Binomial Distribution

Answer: (B)

These charts rely on the data behaving as a normal (Gaussian) distribution. The control limits are drawn using the process mean and standard deviation, typically at plus or minus 2 standard deviations and 3 standard deviations. For a normal distribution, about 95% of in-control measurements fall within ±2 SD and about 99.7% within ±3 SD, so points outside these limits suggest the process may be out of control and needs investigation. Because this interpretation depends on the symmetry and probability properties of the normal distribution, Levey-Jennings charts are tied to Gaussian behavior. If the data followed a different distribution, the likelihood of points landing near or beyond those limits would change, making the same limits less meaningful.