What does the interquartile range (IQR) measure?

The interquartile range (IQR) is a measure of statistical dispersion that specifically focuses on the middle 50% of a data set. It is calculated by taking the difference between the third quartile (Q3) and the first quartile (Q1). This range provides insight into the spread of the central portion of the data, effectively illustrating how much variability exists among the data points that lie in this middle section.

By concentrating on the first and third quartiles, the IQR is not influenced by outliers or extreme values, which might skew the overall perception of the spread when considering the total range of the data. This makes it particularly helpful in understanding the distribution of the data without being affected by those outlier data points that could misrepresent the overall variation.

The other options illustrate different concepts: the total range looks at the entire span from the minimum to maximum values; the difference between the highest and lowest values is essentially the total range; and the average reflects a central tendency rather than spread. Thus, the correct choice highlights the IQR's specific focus on the range of values in the interquartile section of the data set.