Final answer:
The upper and lower quartiles are the medians of each half of the data, excluding the dataset's overall median.
Step-by-step explanation:
The upper and lower quartiles of a dataset are essentially the medians of each half of the data. When we divide a dataset into two equal halves, the first quartile (Q1) is the median of the lower half, and the third quartile (Q3) is the median of the upper half. It's important to note that the actual median of the dataset, also known as the second quartile (Q2), is not included when we calculate Q1 and Q3. For example, if we have a dataset and the median is 7, to find the first quartile, we look at the lower half of the data, which may contain seven values, and the middle value of those seven is Q1. Conversely, for the third quartile, we look at the upper half, and the middle value is Q3. Therefore, the correct choice for the question is C. median.