If the data from a valid measurement system showed the number of balance inquiry calls to a call center varied greatly on two different days when the answering of calls had been changed to a new department, it would be due to...

The situation described indicates that there was a significant change in the number of balance inquiry calls due to the shifting of call responsibilities to a new department. This change to the process can directly influence how calls are handled, potentially altering the volume of inquiries received.

When a new department takes over call answering, different staff members with varying levels of experience or different procedures may be employed, which can lead to fluctuations in call handling efficiency and customer response. These changes can consequently result in variations in the volume of calls.

The other options do not adequately capture the primary reason for the observed variation in call volume. For instance, expected variation refers to natural fluctuations that occur in any system over time, but in this case, the variation is explicitly linked to the change in the process of call handling. Changes to the measurement system would imply that the method of data collection or analysis altered, which is not indicated here. Similarly, a change to the calendar would imply seasonal or time-of-year factors affecting call volumes, but the question specifies that the variation occurred due to a process change, meaning that linking it to calendar timing wouldn’t be accurate.