Final answer:
A repeated deviation away from the mean in QC data is known as a trend. This data pattern indicates a potential systematic issue in the process being measured. In contrast, the mean is the average value of a dataset.
Step-by-step explanation:
A progressive change in QC data all in one direction away from the mean for at least 3 days is a trend. In the context of Quality Control (QC), a trend indicates a systematic deviation from the norm, which could signal a process that is out of control. In other words, it's a continuous increase or decrease in the value being measured.
For example, if the instructor's sample produces a mean number of days absent of 3.5 days, this value represents the average or central tendency of the dataset. It is the arithmetic mean, which is calculated by summing the total number of absent days and dividing by the number of observations.