Which condition is indicated by six consecutive points on one side of the mean?

• A. Shift
• B. Trend
• C. Random error
• D. Calibration drift

Answer: (A)

Seeing six consecutive results on the same side of the mean signals a shift in the process mean. In quality control, the data are expected to fluctuate randomly around a fixed center. When a block of six points all lies above (or below) the established mean, it suggests the central tendency has moved to a new level and the old mean is no longer representative.

A trend involves a consistent directional change over time (steadily increasing or decreasing), which is a different pattern from a single, persistent bias relative to the original mean. Random error would produce points scattered above and below the mean without a persistent bias. Calibration drift implies a gradual, time-based change in instrument response, not a sudden block of six consecutive points on one side.