The middle 50% of your data is called the interquartile range, or IQR. The interquartile range is the distance between the first quartile (Q1) and the third quartile (Q3). This is the same as the distance between the 25th and 75th percentiles. IQR is useful for determining the relative position of your data values. For instance, data values outside the interval Q1 – (1.5 * IQR) and Q3 + (1.5 * IQR) are often considered outliers.

Technically, IQR is a measure of dispersion because it measures the spread of the middle half or middle 50% of your data (between Q1 and Q3). IQR is less sensitive to outliers than the range because it doesn’t include the more extreme values in your dataset.

Five Number Summary

you can summarize the major divisions in your dataset with the five number summary. The five numbers include:

• The minimum
• The first quartile (Q1)
• The median, or second quartile (Q2)
• The third quartile (Q3)
• The maximum

The box part of the box plot goes from Q1 to Q3. The vertical line in the middle of the box is the median (Q2). The horizontal lines on each side of the box, known as whiskers, go from Q1 to the minimum, and from Q3 to the maximum.