What factor should be considered when choosing between the median or mean as a description of the center of a data set?

The correct answer is:

You should consider whether there is an outlier.

Explanation:

In order to find the mean, we add together all of the data points and divide by the number of data points. If there is an outlier, a number much higher or much lower than the rest of the data, this will cause the sum of the data to be affected, which will cause the mean to either be higher or lower than it would without the outlier.

The median, however, is not affected much by outliers, as the median is just the middle value in a set of data.