An abrupt change from the established mean on a QC chart is called what?

• A. Shift
• B. Trend
• C. Cusum
• D. Dispersion

Answer: (A)

An abrupt change in the process mean on a QC chart is called a shift. The center line represents the established mean, and when the data jump to a new level and stay there, the mean has shifted. This is different from a trend, which would show a steady rise or fall over several points rather than a single sudden change. It’s also not about detecting small, gradual deviations (that’s what a cusum does) and not about how spread out the data are around the mean (dispersion concerns variability, not the mean’s location). In practice, you might see several consecutive points clustering on one side of the center line or a clear jump to a higher or lower level, signaling a shift that may warrant investigation.